C Programming Language || Hands On Coding

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int *data;
    int front;
    int rear;
    int capacity;
} Queue;

Queue* createQueue(int capacity) {
    Queue* queue = (Queue*)malloc(sizeof(Queue));
    queue->capacity = capacity;
    queue->data = (int*)malloc(queue->capacity * sizeof(int));
    queue->front = queue->rear = -1;
    return queue;
}

int isQueueEmpty(Queue* queue) {
    return (queue->front == -1);
}

int isQueueFull(Queue* queue) {
    return ((queue->rear + 1) % queue->capacity == queue->front);
}

void enqueue(Queue* queue, int item) {
    if (isQueueFull(queue)) {
        printf("Queue is fulln");
        return;
    }
    if (isQueueEmpty(queue)) {
        queue->front = 0;
    }
    queue->rear = (queue->rear + 1) % queue->capacity;
    queue->data[queue->rear] = item;
}

int dequeue(Queue* queue) {
    if (isQueueEmpty(queue)) {
        printf("Queue is emptyn");
        return -1;
    }
    int item = queue->data[queue->front];
    if (queue->front == queue->rear) {
        queue->front = queue->rear = -1;
    } else {
        queue->front = (queue->front + 1) % queue->capacity;
    }
    return item;
}

typedef struct {
    Queue *q1, *q2;
    int capacity;
} Stack;

Stack* createStack(int capacity) {
    Stack* stack = (Stack*)malloc(sizeof(Stack));
    stack->capacity = capacity;
    stack->q1 = createQueue(capacity);
    stack->q2 = createQueue(capacity);
    return stack;
}

void push(Stack* stack, int item) {
    enqueue(stack->q1, item);
}

int pop(Stack* stack) {
    if (isQueueEmpty(stack->q1)) {
        printf("Stack is emptyn");
        return -1;
    }
    while (stack->q1->front != stack->q1->rear) {
        enqueue(stack->q2, dequeue(stack->q1));
    }
    int item = dequeue(stack->q1);

    Queue* temp = stack->q1;
    stack->q1 = stack->q2;
    stack->q2 = temp;

    return item;
}

int main() {
    Stack* stack = createStack(10);

    push(stack, 10);
    push(stack, 20);
    push(stack, 30);

    printf("%d popped from stackn", pop(stack));
    printf("%d popped from stackn", pop(stack));
    printf("%d popped from stackn", pop(stack));

    return 0;
}

30 popped from stack
20 popped from stack
10 popped from stack

#include <stdio.h>
#include <stdlib.h>

#define MAX_SIZE 100

typedef struct {
    int arr[MAX_SIZE];
    int front;
    int rear;
} Queue;

void initializeQueue(Queue *q) {
    q->front = -1;
    q->rear = -1;
}

int isEmpty(Queue *q) {
    return (q->front == -1);
}

int isFull(Queue *q) {
    return ((q->rear + 1) % MAX_SIZE == q->front);
}

void enqueue(Queue *q, int value) {
    if (isFull(q)) {
        printf("Queue is full!n");
        return;
    }
    if (isEmpty(q)) {
        q->front = 0;
    }
    q->rear = (q->rear + 1) % MAX_SIZE;
    q->arr[q->rear] = value;
}

int dequeue(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty!n");
        return -1;
    }
    int value = q->arr[q->front];
    if (q->front == q->rear) {
        initializeQueue(q);
    } else {
        q->front = (q->front + 1) % MAX_SIZE;
    }
    return value;
}

void reverseFirstK(Queue *q, int k) {
    if (isEmpty(q) || k > (q->rear - q->front + 1 + MAX_SIZE) % MAX_SIZE || k <= 0) {
        return;
    }

    int stack[k];
    for (int i = 0; i < k; i++) {
        stack[i] = dequeue(q);
    }

    for (int i = k - 1; i >= 0; i--) {
        enqueue(q, stack[i]);
    }

    for (int i = 0; i < (q->rear - q->front + 1 + MAX_SIZE) % MAX_SIZE - k; i++) {
        enqueue(q, dequeue(q));
    }
}

void displayQueue(Queue *q) {
    if (isEmpty(q)) {
        printf("Queue is empty!n");
        return;
    }
    printf("Queue: ");
    int i = q->front;
    while (i != q->rear) {
        printf("%d ", q->arr[i]);
        i = (i + 1) % MAX_SIZE;
    }
    printf("%dn", q->arr[q->rear]);
}

int main() {
    Queue q;
    initializeQueue(&q);

    enqueue(&q, 10);
    enqueue(&q, 20);
    enqueue(&q, 30);
    enqueue(&q, 40);
    enqueue(&q, 50);

    printf("Original ");
    displayQueue(&q);

    int k = 3;
    reverseFirstK(&q, k);

    printf("After reversing first %d elements: ", k);
    displayQueue(&q);

    return 0;
}

Original Queue: 10 20 30 40 50
After reversing first 3 elements: Queue: 30 20 10 40 50

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    char* data;
    struct Node* next;
} Node;

typedef struct Queue {
    Node* front;
    Node* rear;
} Queue;

Queue* createQueue() {
    Queue* q = (Queue*)malloc(sizeof(Queue));
    q->front = q->rear = NULL;
    return q;
}

void enqueue(Queue* q, char* data) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    newNode->data = data;
    newNode->next = NULL;
    if (q->rear == NULL) {
        q->front = q->rear = newNode;
        return;
    }
    q->rear->next = newNode;
    q->rear = newNode;
}

char* dequeue(Queue* q) {
    if (q->front == NULL)
        return NULL;
    Node* temp = q->front;
    char* data = temp->data;
    q->front = q->front->next;
    if (q->front == NULL)
        q->rear = NULL;
    free(temp);
    return data;
}

int main() {
    int n;
    scanf("%d", &n);

    Queue* q = createQueue();

    enqueue(q, "1");

    for (int i = 0; i < n; i++) {
        char* current = dequeue(q);
        printf("%s ", current);

        char* s1 = (char*)malloc(sizeof(char) * 20);
        char* s2 = (char*)malloc(sizeof(char) * 20);

        sprintf(s1, "%s0", current);
        sprintf(s2, "%s1", current);
        enqueue(q, s1);
        enqueue(q, s2);
    }
    printf("n");

    return 0;
}

Input: 5
Output: 1 10 11 100 101

#include <stdio.h>
#include <stdlib.h>

#define MAX_SIZE 100

struct PriorityQueue {
    int items[MAX_SIZE];
    int priorities[MAX_SIZE];
    int size;
};

void initialize(struct PriorityQueue *pq) {
    pq->size = 0;
}

int isEmpty(struct PriorityQueue *pq) {
    return (pq->size == 0);
}

int isFull(struct PriorityQueue *pq) {
    return (pq->size == MAX_SIZE);
}

void enqueue(struct PriorityQueue *pq, int item, int priority) {
    if (isFull(pq)) {
        printf("Queue is full!n");
        return;
    }

    int i = pq->size - 1;
    while (i >= 0 && priority < pq->priorities[i]) {
        pq->items[i + 1] = pq->items[i];
        pq->priorities[i + 1] = pq->priorities[i];
        i--;
    }
    pq->items[i + 1] = item;
    pq->priorities[i + 1] = priority;
    pq->size++;
    printf("Enqueued item: %d with priority: %dn", item, priority);
}

int dequeue(struct PriorityQueue *pq) {
    if (isEmpty(pq)) {
        printf("Queue is empty!n");
        return -1;
    }

    int item = pq->items[0];
    for (int i = 0; i < pq->size - 1; i++) {
        pq->items[i] = pq->items[i + 1];
        pq->priorities[i] = pq->priorities[i + 1];
    }
    pq->size--;
    printf("Dequeued item: %dn", item);
    return item;
}

void display(struct PriorityQueue *pq) {
    if (isEmpty(pq)) {
        printf("Queue is empty!n");
        return;
    }

    printf("Queue: ");
    for (int i = 0; i < pq->size; i++) {
        printf("%d (Priority: %d) ", pq->items[i], pq->priorities[i]);
    }
    printf("n");
}

int main() {
    struct PriorityQueue pq;
    initialize(&pq);

    enqueue(&pq, 10, 2);
    enqueue(&pq, 30, 1);
    enqueue(&pq, 20, 3);
    display(&pq);

    dequeue(&pq);
    display(&pq);

    return 0;
}

Enqueued item: 10 with priority: 2
Enqueued item: 30 with priority: 1
Enqueued item: 20 with priority: 3
Queue: 30 (Priority: 1) 10 (Priority: 2) 20 (Priority: 3)
Dequeued item: 30
Queue: 10 (Priority: 2) 20 (Priority: 3)

#include <stdio.h>
#include <stdlib.h>

#define MAX_SIZE 5

int queue[MAX_SIZE];
int front = -1;
int rear = -1;

void enqueue(int value) {
    if ((rear + 1) % MAX_SIZE == front) {
        printf("Queue is fulln");
        return;
    } else if (front == -1) {
        front = 0;
        rear = 0;
    } else {
        rear = (rear + 1) % MAX_SIZE;
    }
    queue[rear] = value;
    printf("Inserted %dn", value);
}

int dequeue() {
    int value;
    if (front == -1) {
        printf("Queue is emptyn");
        return -1;
    }

    value = queue[front];
    if (front == rear) {
        front = -1;
        rear = -1;
    } else {
        front = (front + 1) % MAX_SIZE;
    }
    printf("Deleted %dn", value);
    return value;
}

void display() {
    int i;
    if (front == -1) {
        printf("Queue is emptyn");
        return;
    }
    printf("Queue elements are:n");
    for (i = front; i != rear; i = (i + 1) % MAX_SIZE)
        printf("%d ", queue[i]);
    printf("%d ", queue[rear]);
    printf("n");
}

int main() {
    int choice, value;

    while (1) {
        printf("1. Enqueuen");
        printf("2. Dequeuen");
        printf("3. Displayn");
        printf("4. Exitn");
        printf("Enter your choice: ");
        scanf("%d", &choice);

        switch (choice) {
            case 1:
                printf("Enter value to enqueue: ");
                scanf("%d", &value);
                enqueue(value);
                break;
            case 2:
                dequeue();
                break;
            case 3:
                display();
                break;
            case 4:
                exit(0);
            default:
                printf("Invalid choicen");
        }
    }

    return 0;
}

1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 10
Output: Inserted 10
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 20
Output: Inserted 20
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 30
Output: Inserted 30
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 40
Output: Inserted 40
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 50
Output: Inserted 50
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 60
Output: Queue is full
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Output: Queue elements are:
10 20 30 40 50
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 10
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Output: Queue elements are:
20 30 40 50
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 60
Output: Inserted 60
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Output: Queue elements are:
20 30 40 50 60
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 20
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 30
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 40
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 50
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Deleted 60
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Output: Queue is empty
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Output: Queue is empty
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 4

#include <stdio.h>
#include <stdlib.h>

typedef struct Node {
    int data;
    struct Node* next;
} Node;

typedef struct Queue {
    Node* front;
    Node* rear;
} Queue;

Queue* createQueue() {
    Queue* q = (Queue*)malloc(sizeof(Queue));
    if (q == NULL) {
        printf("Memory allocation failedn");
        exit(EXIT_FAILURE);
    }
    q->front = q->rear = NULL;
    return q;
}

void enqueue(Queue* q, int data) {
    Node* newNode = (Node*)malloc(sizeof(Node));
    if (newNode == NULL) {
        printf("Memory allocation failedn");
        exit(EXIT_FAILURE);
    }
    newNode->data = data;
    newNode->next = NULL;

    if (q->rear == NULL) {
        q->front = q->rear = newNode;
        return;
    }

    q->rear->next = newNode;
    q->rear = newNode;
}

int dequeue(Queue* q) {
    if (q->front == NULL) {
        printf("Queue is emptyn");
        return -1;
    }

    Node* temp = q->front;
    int data = temp->data;

    q->front = q->front->next;

    if (q->front == NULL) {
        q->rear = NULL;
    }

    free(temp);
    return data;
}

int isEmpty(Queue* q) {
    return (q->front == NULL);
}

void displayQueue(Queue* q) {
    Node* current = q->front;
    if (current == NULL) {
        printf("Queue is emptyn");
        return;
    }
    printf("Queue elements: ");
    while (current != NULL) {
        printf("%d ", current->data);
        current = current->next;
    }
    printf("n");
}

int main() {
    Queue* q = createQueue();

    enqueue(q, 10);
    enqueue(q, 20);
    enqueue(q, 30);

    displayQueue(q);

    printf("Dequeued: %dn", dequeue(q));
    printf("Dequeued: %dn", dequeue(q));

    displayQueue(q);

    if (isEmpty(q)) {
        printf("Queue is emptyn");
    } else {
        printf("Queue is not emptyn");
    }

    printf("Dequeued: %dn", dequeue(q));

    if (isEmpty(q)) {
        printf("Queue is emptyn");
    } else {
        printf("Queue is not emptyn");
    }
     dequeue(q);

    return 0;
}

Queue elements: 10 20 30
Dequeued: 10
Dequeued: 20
Queue elements: 30
Queue is not empty
Dequeued: 30
Queue is empty
Queue is empty

#include <stdio.h>
#include <stdlib.h>

#define MAX_SIZE 100

int queue[MAX_SIZE];
int front = -1;
int rear = -1;

void enqueue(int value) {
  if (rear == MAX_SIZE - 1) {
    printf("Queue is full!n");
  } else {
    if (front == -1)
      front = 0;
    rear++;
    queue[rear] = value;
    printf("Inserted %d into queuen", value);
  }
}

void dequeue() {
  if (front == -1 || front > rear) {
    printf("Queue is empty!n");
  } else {
    printf("Deleted element: %dn", queue[front]);
    front++;
  }
}

void display() {
  if (front == -1) {
    printf("Queue is empty!n");
  } else {
    printf("Queue elements are:n");
    for (int i = front; i <= rear; i++)
      printf("%d ", queue[i]);
    printf("n");
  }
}

int main() {
  int choice, value;
  while (1) {
    printf("1. Enqueuen");
    printf("2. Dequeuen");
    printf("3. Displayn");
    printf("4. Exitn");
    printf("Enter your choice: ");
    scanf("%d", &choice);

    switch (choice) {
      case 1:
        printf("Enter value to enqueue: ");
        scanf("%d", &value);
        enqueue(value);
        break;
      case 2:
        dequeue();
        break;
      case 3:
        display();
        break;
      case 4:
        exit(0);
      default:
        printf("Wrong choicen");
    }
  }
  return 0;
}

1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 10
Inserted 10 into queue
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 1
Enter value to enqueue: Input: 20
Inserted 20 into queue
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Queue elements are:
10 20
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Deleted element: 10
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Queue elements are:
20
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Deleted element: 20
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 3
Queue is empty!
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 2
Queue is empty!
1. Enqueue
2. Dequeue
3. Display
4. Exit
Enter your choice: Input: 4

#include <stdio.h>
#include <stdlib.h>

struct Stack {
    int top;
    unsigned capacity;
    int *array;
};

struct Stack* createStack(unsigned capacity) {
    struct Stack* stack = (struct Stack*) malloc(sizeof(struct Stack));
    stack->capacity = capacity;
    stack->top = -1;
    stack->array = (int*) malloc(stack->capacity * sizeof(int));
    return stack;
}

int isFull(struct Stack* stack) {
    return stack->top == stack->capacity - 1;
}

int isEmpty(struct Stack* stack) {
    return stack->top == -1;
}

void push(struct Stack* stack, int item) {
    if (isFull(stack))
        return;
    stack->array[++stack->top] = item;
}

int pop(struct Stack* stack) {
    if (isEmpty(stack))
        return -1; // or some error value
    return stack->array[stack->top--];
}

int peek(struct Stack* stack) {
    if (isEmpty(stack))
        return -1; // or some error value
    return stack->array[stack->top];
}

void sortStack(struct Stack* stack) {
    struct Stack* tempStack = createStack(stack->capacity);
    int tmp;

    while (!isEmpty(stack)) {
        tmp = pop(stack);

        while (!isEmpty(tempStack) && peek(tempStack) > tmp) {
            push(stack, pop(tempStack));
        }

        push(tempStack, tmp);
    }

    while (!isEmpty(tempStack)) {
        push(stack, pop(tempStack));
    }
    free(tempStack->array);
    free(tempStack);
}

int main() {
    struct Stack* stack = createStack(5);
    push(stack, 5);
    push(stack, 2);
    push(stack, 4);
    push(stack, 1);
    push(stack, 3);

    sortStack(stack);

    printf("Sorted stack: ");
    while (!isEmpty(stack)) {
        printf("%d ", pop(stack));
    }
    printf("n");
    free(stack->array);
    free(stack);

    return 0;
}

Sorted stack: 1 2 3 4 5

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define MAX_SIZE 100

struct Stack {
    int arr[MAX_SIZE];
    int top;
};

void initialize(struct Stack *stack) {
    stack->top = -1;
}

bool isEmpty(struct Stack *stack) {
    return stack->top == -1;
}

bool isFull(struct Stack *stack) {
    return stack->top == MAX_SIZE - 1;
}

void push(struct Stack *stack, int value) {
    if (isFull(stack)) {
        printf("Stack Overflown");
        return;
    }
    stack->arr[++stack->top] = value;
}

int pop(struct Stack *stack) {
    if (isEmpty(stack)) {
        printf("Stack Underflown");
        return -1;
    }
    return stack->arr[stack->top--];
}

bool isStackSorted(struct Stack *stack) {
    if (isEmpty(stack) || stack->top == 0) {
        return true;
    }

    struct Stack tempStack;
    initialize(&tempStack);
    int temp;
    bool sorted = true;

    while (!isEmpty(stack)) {
        temp = pop(stack);

        if (!isEmpty(&tempStack) && tempStack.arr[tempStack.top] < temp) {
            sorted = false;
            break;
        }

        while (!isEmpty(&tempStack) && tempStack.arr[tempStack.top] < temp) {
            push(stack, pop(&tempStack));
        }
        push(&tempStack, temp);
    }

    while (!isEmpty(&tempStack)) {
        push(stack, pop(&tempStack));
    }

    return sorted;
}

int main() {
    struct Stack myStack;
    initialize(&myStack);

    push(&myStack, 5);
    push(&myStack, 4);
    push(&myStack, 3);
    push(&myStack, 2);
    push(&myStack, 1);

    if (isStackSorted(&myStack)) {
        printf("Stack is sorted.n");
    } else {
        printf("Stack is not sorted.n");
    }

    return 0;
}

Stack is sorted.

#include <stdio.h>
#include <stdlib.h>

#define SIZE 10

int array[SIZE];
int top1 = -1;
int top2 = SIZE;

void push1(int data) {
    if (top1 < top2 - 1) {
        top1++;
        array[top1] = data;
    } else {
        printf("Stack 1 is fulln");
    }
}

void push2(int data) {
    if (top1 < top2 - 1) {
        top2--;
        array[top2] = data;
    } else {
        printf("Stack 2 is fulln");
    }
}

int pop1() {
    if (top1 >= 0) {
        int popped = array[top1];
        top1--;
        return popped;
    } else {
        printf("Stack 1 is emptyn");
        return -1;
    }
}

int pop2() {
    if (top2 < SIZE) {
        int popped = array[top2];
        top2++;
        return popped;
    } else {
        printf("Stack 2 is emptyn");
        return -1;
    }
}

int main() {
    push1(10);
    push1(20);
    push2(30);
    push2(40);

    printf("Popped from Stack 1: %dn", pop1());
    printf("Popped from Stack 2: %dn", pop2());

    return 0;
}

Popped from Stack 1: 20
Popped from Stack 2: 40

#include <stdio.h>
#include <stdlib.h>

#define MAX_SIZE 100

struct Stack {
    int top;
    int items[MAX_SIZE];
};

void initialize(struct Stack *s) {
    s->top = -1;
}

int isEmpty(struct Stack *s) {
    return (s->top == -1);
}

int isFull(struct Stack *s) {
    return (s->top == MAX_SIZE - 1);
}

void push(struct Stack *s, int data) {
    if (isFull(s)) {
        printf("Stack Overflow n");
        return;
    }
    s->items[++s->top] = data;
}

int pop(struct Stack *s) {
    if (isEmpty(s)) {
        printf("Stack Underflow n");
        return -1;
    }
    return s->items[s->top--];
}

int main() {
    struct Stack s;
    initialize(&s);
    int n, i, num;

    printf("Enter the number of elements in the list: ");
    scanf("%d", &n);

    int list[n];

    printf("Enter the elements of the list:n");
    for (i = 0; i < n; i++) {
        scanf("%d", &list[i]);
    }

    for (i = 0; i < n; i++) {
        push(&s, list[i]);
    }

    printf("Reversed List:n");
    for (i = 0; i < n; i++) {
        list[i] = pop(&s);
        printf("%d ", list[i]);
    }
    printf("n");

    return 0;
}

Input: 5
Input: 1
Input: 2
Input: 3
Input: 4
Input: 5
Output: Enter the number of elements in the list: Enter the elements of the list:
Reversed List:
5 4 3 2 1

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define MAX_SIZE 100

struct Stack {
    char items[MAX_SIZE];
    int top;
};

void initialize(struct Stack *s) {
    s->top = -1;
}

int isEmpty(struct Stack *s) {
    return (s->top == -1);
}

int isFull(struct Stack *s) {
    return (s->top == MAX_SIZE - 1);
}

void push(struct Stack *s, char c) {
    if (isFull(s)) {
        printf("Stack Overflown");
        return;
    }
    s->items[++s->top] = c;
}

char pop(struct Stack *s) {
    if (isEmpty(s)) {
        printf("Stack Underflown");
        return '0';
    }
    return s->items[s->top--];
}

int main() {
    char str[MAX_SIZE];
    struct Stack s;
    initialize(&s);

    printf("Enter a string: ");
    scanf("%s", str);

    int len = strlen(str);

    for (int i = 0; i < len; i++) {
        push(&s, str[i]);
    }

    printf("Reversed string: ");
    for (int i = 0; i < len; i++) {
        printf("%c", pop(&s));
    }
    printf("n");

    return 0;
}

Input: hello
Output: Enter a string: Reversed string: olleh

#include <stdio.h>
#include <stdlib.h>

int main() {
    int n;
    printf("Enter the number of days: ");
    scanf("%d", &n);

    int prices[n];
    printf("Enter the stock prices for each day:n");
    for (int i = 0; i < n; i++) {
        scanf("%d", &prices[i]);
    }

    int span[n];
    for (int i = 0; i < n; i++) {
        span[i] = 1; // Initialize span to 1
        for (int j = i - 1; j >= 0 && prices[j] <= prices[i]; j--) {
            span[i]++;
        }
    }

    printf("Stock Span values:n");
    for (int i = 0; i < n; i++) {
        printf("%d ", span[i]);
    }
    printf("n");

    return 0;
}

Input: 7
Input: 100
Input: 80
Input: 60
Input: 70
Input: 60
Input: 75
Input: 85
Output: Enter the number of days: Enter the stock prices for each day:
Stock Span values:
1 1 1 2 1 4 6

#include <stdio.h>
#include <stdlib.h>

int main() {
    int n;
    printf("Enter the number of elements: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements:n");
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    int nextSmaller[n];
    for (int i = 0; i < n; i++) {
        nextSmaller[i] = -1;
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[i]) {
                nextSmaller[i] = arr[j];
                break;
            }
        }
    }

    printf("Next Smaller Element:n");
    for (int i = 0; i < n; i++) {
        printf("%d ", nextSmaller[i]);
    }
    printf("n");

    return 0;
}

Input: 5
Input: 5
Input: 4
Input: 3
Input: 2
Input: 1
Output: Enter the number of elements: Enter the elements:
Next Smaller Element:
4 3 2 1 -1
Input: 4
Input: 1
Input: 3
Input: 2
Input: 4
Output: Enter the number of elements: Enter the elements:
Next Smaller Element:
-1 2 -1 -1

#include <stdio.h>
#include <stdlib.h>

int main() {
    int n;

    printf("Enter the number of elements: ");
    scanf("%d", &n);

    int arr[n];
    printf("Enter the elements:n");
    for (int i = 0; i < n; i++) {
        scanf("%d", &arr[i]);
    }

    int nextGreater[n];
    for (int i = 0; i < n; i++) {
        nextGreater[i] = -1;
    }

    for (int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (arr[j] > arr[i]) {
                nextGreater[i] = arr[j];
                break;
            }
        }
    }

    printf("Next Greater Elements are:n");
    for (int i = 0; i < n; i++) {
        printf("%d ", nextGreater[i]);
    }
    printf("n");

    return 0;
}

Input: 5
Input: 16 7 2 8 9
Output: Enter the number of elements: Enter the elements:
Next Greater Elements are:
-1 8 8 9 -1

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define MAX_SIZE 100

int stack[MAX_SIZE];
int top = -1;

void push(int value) {
    stack[++top] = value;
}

int pop() {
    return stack[top--];
}

int evaluatePrefix(char* expression) {
    int i, operand1, operand2, result;
    for (i = strlen(expression) - 1; i >= 0; i--) {
        if (isdigit(expression[i])) {
            push(expression[i] - '0');
        } else {
            operand1 = pop();
            operand2 = pop();
            switch (expression[i]) {
                case '+':
                    result = operand1 + operand2;
                    break;
                case '-':
                    result = operand1 - operand2;
                    break;
                case '*':
                    result = operand1 * operand2;
                    break;
                case '/':
                    result = operand1 / operand2;
                    break;
                default:
                    printf("Invalid operatorn");
                    return -1;
            }
            push(result);
        }
    }
    return pop();
}

int main() {
    char expression[MAX_SIZE];

    printf("Enter prefix expression: ");
    scanf("%s", expression);

    int result = evaluatePrefix(expression);

    if (result != -1) {
        printf("Result: %dn", result);
    }

    return 0;
}

Input: +*234
Output: Result: 10

Input: -+*23/825
Output: Result: 6

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

#define MAX_SIZE 100

int stack[MAX_SIZE];
int top = -1;

void push(int value) {
    stack[++top] = value;
}

int pop() {
    return stack[top--];
}

int evaluatePostfix(char* expression) {
    int i = 0;
    while (expression[i] != '0') {
        if (isdigit(expression[i])) {
            int num = 0;
            while(isdigit(expression[i])){
                num = num * 10 + (expression[i] - '0');
                i++;
            }
            i--;
            push(num);
        } else if (expression[i] == '+' || expression[i] == '-' ||
                   expression[i] == '*' || expression[i] == '/') {
            int operand2 = pop();
            int operand1 = pop();
            switch (expression[i]) {
                case '+':
                    push(operand1 + operand2);
                    break;
                case '-':
                    push(operand1 - operand2);
                    break;
                case '*':
                    push(operand1 * operand2);
                    break;
                case '/':
                    push(operand1 / operand2);
                    break;
            }
        }
        i++;
    }
    return pop();
}

int main() {
    char expression[MAX_SIZE];

    printf("Enter postfix expression: ");
    scanf("%s", expression);

    int result = evaluatePostfix(expression);
    printf("Result: %dn", result);

    return 0;
}

Input: 23+
Output: Result: 5
Input: 123+*
Output: Result: 6
Input: 567*+
Output: Result: 47
Input: 102/
Output: Result: 5
Input: 53-
Output: Result: 2
Input: 105+2*
Output: Result: 30
Input: 231*+9-
Output: Result: -4
Input: 123+4*+
Enter postfix expression: 123+4*+
Result: 20

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define MAX_SIZE 100

char stack[MAX_SIZE];
int top = -1;

void push(char c) {
    if (top == MAX_SIZE - 1) {
        printf("Stack Overflown");
        return;
    }
    stack[++top] = c;
}

char pop() {
    if (top == -1) {
        return -1; // Indicates an empty stack
    }
    return stack[top--];
}

int precedence(char operator) {
    switch (operator) {
        case '+':
        case '-':
            return 1;
        case '*':
        case '/':
            return 2;
        case '^':
            return 3;
        default:
            return 0;
    }
}

void reverseString(char *str) {
    int len = strlen(str);
    for (int i = 0, j = len - 1; i < j; i++, j--) {
        char temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}

void infixToPrefix(char *infix, char *prefix) {
    int i, j = 0;
    int len = strlen(infix);

    reverseString(infix);

    for (i = 0; i < len; i++) {
        if (infix[i] == '(') {
            infix[i] = ')';
        } else if (infix[i] == ')') {
            infix[i] = '(';
        }
    }

    for (i = 0; i < len; i++) {
        if (isalnum(infix[i])) {
            prefix[j++] = infix[i];
        } else if (infix[i] == '(') {
            push(infix[i]);
        } else if (infix[i] == ')') {
            while (top != -1 && stack[top] != '(') {
                prefix[j++] = pop();
            }
            if (top != -1 && stack[top] == '(') {
                pop();
            }
        } else {
            while (top != -1 && precedence(infix[i]) <= precedence(stack[top])) {
                prefix[j++] = pop();
            }
            push(infix[i]);
        }
    }

    while (top != -1) {
        prefix[j++] = pop();
    }

    prefix[j] = '0';
    reverseString(prefix);
}

int main() {
    char infix[MAX_SIZE];
    char prefix[MAX_SIZE];

    printf("Enter infix expression: ");
    scanf("%s", infix);

    infixToPrefix(infix, prefix);

    printf("Prefix expression: %sn", prefix);

    return 0;
}

Input: a+b*c
Output: Prefix expression: +a*bc

Input: (a+b)*c
Output: Prefix expression: *+abc

Input: a+b*(c^d-e)^(f+g*h)-i
Output: Prefix expression: -+a*b^-^cde+f*ghi

Input: A*(B+C)/D
Output: Prefix expression: /*A+BCD

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define MAX_SIZE 100

char stack[MAX_SIZE];
int top = -1;

void push(char item) {
  stack[++top] = item;
}

char pop() {
  if (top == -1) {
    return -1;
  }
  return stack[top--];
}

int precedence(char operator) {
  switch (operator) {
    case '+':
    case '-':
      return 1;
    case '*':
    case '/':
      return 2;
    case '^':
      return 3;
    default:
      return 0;
  }
}

int main() {
  char infix[MAX_SIZE], postfix[MAX_SIZE];
  int i, j = 0;

  printf("Enter infix expression: ");
  scanf("%s", infix);

  for (i = 0; infix[i] != '0'; i++) {
    if (isalnum(infix[i])) {
      postfix[j++] = infix[i];
    } else if (infix[i] == '(') {
      push(infix[i]);
    } else if (infix[i] == ')') {
      while (top != -1 && stack[top] != '(') {
        postfix[j++] = pop();
      }
      pop(); // Remove the '('
    } else {
      while (top != -1 && precedence(infix[i]) <= precedence(stack[top])) {
        postfix[j++] = pop();
      }
      push(infix[i]);
    }
  }

  while (top != -1) {
    postfix[j++] = pop();
  }

  postfix[j] = '0';

  printf("Postfix expression: %sn", postfix);

  return 0;
}

Input: a+b*c
Output: abc*+
Input: (a+b)*c
Output: ab+c*
Input: a+b*(c^d-e)^(f+g*h)-i
Output: abcd^e-fgh*+^*+i-
Input: a*b+c/d
Output: ab*cd/+
Input: a^b^c
Output: abc^^