AI Coding & CSE Fundamentals

Left Rotate Array by 1 Position

#include <stdio.h>

void leftRotate(int arr[], int n) {
 int temp = arr[0];
 for (int i = 0; i < n - 1; i++) {
 arr[i] = arr[i+1];
 }
 arr[n-1] = temp;
}

int main() {
 int arr[] = {1, 2, 3, 4, 5};
 int n = sizeof(arr) / sizeof(arr[0]);

 leftRotate(arr, n);

 for (int i = 0; i < n; i++) {
 printf("%d ", arr[i]);
 }
 printf("\n");
 return 0;
}

Find the First Non-Repeating Element in an Array

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 1, 2, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    int i, j, found = 0;

    for (i = 0; i < size; i++) {
        int count = 0;
        for (j = 0; j < size; j++) {
            if (arr[i] == arr[j]) {
                count++;
            }
        }
        if (count == 1) {
            printf("First non-repeating element: %d\n", arr[i]);
            found = 1;
            break;
        }
    }

    if (!found) {
        printf("No non-repeating element found.\n");
    }

    return 0;
}

First Repeating Element in an Array

#include <stdio.h>

int main() {
    int arr[] = {10, 5, 3, 4, 3, 5, 6};
    int size = sizeof(arr) / sizeof(arr[0]);
    int i, j;

    for (i = 0; i < size; i++) {
        for (j = i + 1; j < size; j++) {
            if (arr[i] == arr[j]) {
                printf("First repeating element: %d\n", arr[i]);
                return 0;
            }
        }
    }

    printf("No repeating element found.\n");
    return 0;
}

Count Frequency of Each Element in an Array

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 1, 2, 4, 1, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    int freq[100] = {0}; 

    for (int i = 0; i < size; i++) {
        freq[arr[i]]++;
    }

    for (int i = 0; i < 100; i++) {
        if (freq[i] > 0) {
            printf("Element %d: %d\n", i, freq[i]);
        }
    }

    return 0;
}

Second Largest and Second Smallest Element in an Array

#include <stdio.h>
#include <limits.h>

int main() {
    int arr[] = {12, 35, 1, 10, 34, 1};
    int n = sizeof(arr) / sizeof(arr[0]);

    int largest = INT_MIN, secondLargest = INT_MIN;
    int smallest = INT_MAX, secondSmallest = INT_MAX;

    for (int i = 0; i < n; i++) {
        if (arr[i] > largest) {
            secondLargest = largest;
            largest = arr[i];
        } else if (arr[i] > secondLargest && arr[i] != largest) {
            secondLargest = arr[i];
        }

        if (arr[i] < smallest) {
            secondSmallest = smallest;
            smallest = arr[i];
        } else if (arr[i] < secondSmallest && arr[i] != smallest) {
            secondSmallest = arr[i];
        }
    }

    printf("Second Largest: %d\n", secondLargest);
    printf("Second Smallest: %d\n", secondSmallest);

    return 0;
}

Find Unique Elements in Array

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 2, 3, 4, 4, 5};
    int size = sizeof(arr) / sizeof(arr[0]);
    int unique[size];
    int unique_count = 0;
    int is_unique;

    for (int i = 0; i < size; i++) {
        is_unique = 1;
        for (int j = 0; j < unique_count; j++) {
            if (arr[i] == unique[j]) {
                is_unique = 0;
                break;
            }
        }
        if (is_unique) {
            unique[unique_count] = arr[i];
            unique_count++;
        }
    }

    printf("Unique elements: ");
    for (int i = 0; i < unique_count; i++) {
        printf("%d ", unique[i]);
    }
    printf("\n");

    return 0;
}

Find Duplicate Elements in an Array

#include <stdio.h>

int main() {
    int arr[] = {1, 2, 3, 4, 2, 5, 6, 3};
    int n = sizeof(arr) / sizeof(arr[0]);
    int i, j;

    printf("Duplicate elements: ");
    for (i = 0; i < n; i++) {
        for (j = i + 1; j < n; j++) {
            if (arr[i] == arr[j]) {
                printf("%d ", arr[i]);
                break;
            }
        }
    }
    printf("\n");
    return 0;
}

Binary Search in a Sorted Array

#include <stdio.h>

int binarySearch(int arr[], int left, int right, int target) {
    while (left <= right) {
        int mid = left + (right - left) / 2;

        if (arr[mid] == target)
            return mid;

        if (arr[mid] < target)
            left = mid + 1;
        else
            right = mid - 1;
    }
    return -1;
}

int main() {
    int arr[] = {2, 3, 4, 10, 40};
    int n = sizeof(arr) / sizeof(arr[0]);
    int target = 10;
    int result = binarySearch(arr, 0, n - 1, target);
    if (result == -1)
        printf("Element is not present in array");
    else
        printf("Element is present at index %d", result);
    return 0;
}

Search an Element in a 1D Array (Linear Search)

#include <stdio.h>

int main() {
    int arr[] = {2, 4, 6, 8, 10};
    int size = sizeof(arr) / sizeof(arr[0]);
    int key, i, found = 0;

    printf("Enter element to search: ");
    scanf("%d", &key);

    for (i = 0; i < size; i++) {
        if (arr[i] == key) {
            found = 1;
            printf("Element found at index %d\n", i);
            break;
        }
    }

    if (!found) {
        printf("Element not found.\n");
    }

    return 0;
}

Reverse an Array

#include <stdio.h>

void reverseArray(int arr[], int size) {
 int start = 0;
 int end = size - 1;
 int temp;

 while (start < end) {
 temp = arr[start];
 arr[start] = arr[end];
 arr[end] = temp;
 start++;
 end--;
 }
}

int main() {
 int arr[] = {1, 2, 3, 4, 5};
 int size = sizeof(arr) / sizeof(arr[0]);

 reverseArray(arr, size);

 for (int i = 0; i < size; i++) {
 printf("%d ", arr[i]);
 }
 printf("\n");
 return 0;
}

Array Sum and Average

#include <stdio.h>

int main() {
 int arr[5] = {10, 20, 30, 40, 50};
 int sum = 0;
 float avg;

 for (int i = 0; i < 5; i++) {
 sum += arr[i];
 }

 avg = (float)sum / 5;

 printf("Sum: %d\n", sum);
 printf("Average: %.2f\n", avg);

 return 0;
}

Find Maximum and Minimum in an Array

#include <stdio.h>

int main() {
  int arr[] = {5, 2, 9, 1, 5, 6};
  int n = sizeof(arr) / sizeof(arr[0]);
  int max = arr[0];
  int min = arr[0];

  for (int i = 1; i < n; i++) {
    if (arr[i] > max) {
      max = arr[i];
    }
    if (arr[i] < min) {
      min = arr[i];
    }
  }

  printf("Maximum: %d\n", max);
  printf("Minimum: %d\n", min);
  return 0;
}

Input and Print Array Elements

#include <stdio.h>

int main() {
    int arr[5];
    int i;

    printf("Enter 5 integer elements:\n");
    for (i = 0; i < 5; i++) {
        scanf("%d", &arr[i]);
    }

    printf("Array elements are: \n");
    for (i = 0; i < 5; i++) {
        printf("%d ", arr[i]);
    }
    printf("\n");

    return 0;
}

e 5). This can lead to unexpected behavior or crashes! - **Array Size:** The size of an array must be known at compile time (unless you are using dynamic memory allocation which is a more advanced topic). - **Memory Allocation:** Arrays consume memory. Larger arrays require more memory. ✅ **Best Practices:** - **Meaningful Names:** Use descriptive names for your arrays. - **Comments:** Add comments to explain what your code does. - **Error Handling:** Implement checks to prevent out-of-bounds access and other potential errors. 💡 **Tips:** - Practice, practice, practice! The more you work with arrays, the better you'll understand them. - Draw diagrams to visualize how arrays are structured in memory. - Experiment with different operations to see how they work. Arrays are powerful tools for organizing and manipulating data. Master them, and you'll be well on your way to becoming a proficient C programmer! 🎉

Let's dive into the world of Arrays in C! 🚀 This is a fundamental concept for organizing data, so pay close attention! **What is an Array?** 🧠 Think of an array as a container holding multiple values of the *same* data type (like `int`, `float`, `char`) under a single variable name. It's like a neatly organized row of boxes where each box holds a piece of information. **1D Arrays (One-Dimensional)** 🧱 A 1D array is the simplest type. Imagine a straight line of boxes. - **Declaration:** `data_type array_name[array_size];` Example: `int numbers[5];` -> This creates an array named `numbers` that can hold 5 integers. - **Accessing Elements:** Array elements are accessed using their *index*, starting from 0. So, `numbers[0]` is the first element, `numbers[1]` is the second, and so on. - **Initialization:** You can initialize an array when you declare it: `int numbers[5] = {10, 20, 30, 40, 50};` - **Example:** Let's print the elements of our `numbers` array:

#include <stdio.h>

int main() {
  int numbers[5] = {10, 20, 30, 40, 50};
  for (int i = 0; i < 5; i++) {
    printf("Element at index %d: %dn", i, numbers[i]);
  }
  return 0;
}

**2D Arrays (Two-Dimensional)** 🏢 A 2D array is like a table or a grid, with rows and columns. It's essentially an array of arrays! - **Declaration:** `data_type array_name[number_of_rows][number_of_columns];` Example: `int matrix[3][4];` -> This creates a 2D array named `matrix` with 3 rows and 4 columns. - **Accessing Elements:** You need two indices: one for the row and one for the column. `matrix[0][0]` is the element at the first row and first column. `matrix[1][2]` is the element at the second row and third column. - **Initialization:** `int matrix[3][4] = { {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12} };` - **Example:** Let's print the elements of our `matrix` array:

#include <stdio.h>

int main() {
  int matrix[3][4] = { {1, 2, 3, 4}, {5, 6, 7, 8}, {9, 10, 11, 12} };

  for (int i = 0; i < 3; i++) { // Loop through rows
    for (int j = 0; j < 4; j++) { // Loop through columns
      printf("Element at matrix[%d][%d]: %dn", i, j, matrix[i][j]);
    }
  }
  return 0;
}

**Working with Arrays (Without Sorting)** 🛠️ Here are some common operations you can perform on arrays: - **Searching:** Finding a specific element in an array.

#include <stdio.h>

int main() {
  int numbers[5] = {10, 20, 30, 40, 50};
  int search_value = 30;
  int found = 0;

  for (int i = 0; i < 5; i++) {
    if (numbers[i] == search_value) {
      printf("Value %d found at index %dn", search_value, i);
      found = 1;
      break; // Exit the loop once found
    }
  }

  if (!found) {
    printf("Value %d not found in the arrayn", search_value);
  }
  return 0;
}

- **Frequency:** Counting how many times an element appears in an array.

#include <stdio.h>

int main() {
  int numbers[10] = {1, 2, 2, 3, 3, 3, 4, 4, 4, 4};
  int frequency[5] = {0}; // Initialize frequency array (assuming values are between 1-4)

  for (int i = 0; i < 10; i++) {
    frequency[numbers[i]]++; // Increment the frequency count for the current number
  }

  for (int i = 1; i < 5; i++) {
    printf("Frequency of %d: %dn", i, frequency[i]);
  }
  return 0;
}

- **Matrix Operations (2D Arrays):** Common operations include addition, subtraction, and multiplication of matrices.

#include <stdio.h>

int main() {
  int matrix1[2][2] = {{1, 2}, {3, 4}};
  int matrix2[2][2] = {{5, 6}, {7, 8}};
  int sum_matrix[2][2];

  // Matrix Addition
  for (int i = 0; i < 2; i++) {
    for (int j = 0; j < 2; j++) {
      sum_matrix[i][j] = matrix1[i][j] + matrix2[i][j];
      printf("%d ",sum_matrix[i][j]);
    }
  }

  return 0;
}

⚠️ **Important Notes:** - **Array Bounds:** Be careful not to access elements outside the array's boundaries (e.g., `numbers[5]` in an array of siz

Mutual Recursion: is_even() and is_odd()

#include <stdio.h>

int is_even(int n);
int is_odd(int n);

int is_even(int n) {
  if (n == 0) return 1;
  return is_odd(n - 1);
}

int is_odd(int n) {
  if (n == 0) return 0;
  return is_even(n - 1);
}

int main() {
  int num = 7;
  if (is_even(num)) {
    printf("%d is even.\n", num);
  } else {
    printf("%d is odd.\n", num);
  }
  return 0;
}

Palindrome String Check using Recursion

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

int isPalindrome(char str[], int start, int end) {
    if (start >= end) {
        return 1;
    }
    if (str[start] != str[end]) {
        return 0;
    }
    return isPalindrome(str, start + 1, end - 1);
}

int main() {
    char str[100];
    scanf("%s", str);
    int n = strlen(str);
    if (isPalindrome(str, 0, n - 1)) {
        printf("Palindrome");
    } else {
        printf("Not Palindrome");
    }
    return 0;
}

Decimal to Binary Conversion using Recursion

#include <stdio.h>

void decimalToBinary(int n) {
  if (n == 0) {
    return;
  }
  decimalToBinary(n / 2);
  printf("%d", n % 2);
}

int main() {
  int decimal;
  printf("Enter a decimal number: ");
  scanf("%d", &decimal);
  if (decimal == 0) {
      printf("0");
  } else {
    decimalToBinary(decimal);
  }
  printf("\n");
  return 0;
}

Print Numbers from N to 1 Using Recursion

#include <stdio.h>

void printNumbers(int n) {
  if (n > 0) {
    printf("%d ", n);
    printNumbers(n - 1);
  }
}

int main() {
  int n;
  scanf("%d", &n);
  printNumbers(n);
  printf("\n");
  return 0;
}