C Programming Codes

String Case Conversion

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

int main() {
 char str[100];
 int i;

 printf("Enter a string: ");
 fgets(str, sizeof(str), stdin);
 str[strcspn(str, "\n")] = 0;

 for (i = 0; str[i] != '\0'; i++) {
 if (islower(str[i])) {
 str[i] = toupper(str[i]);
 } else if (isupper(str[i])) {
 str[i] = tolower(str[i]);
 }
 }

 printf("Modified string: %s\n", str);
 return 0;
}

Compare Two Strings (Without strcmp)

#include <stdio.h>

int main() {
 char str1[100], str2[100];
 int i = 0, flag = 0;

 scanf("%s", str1);
 scanf("%s", str2);

 while (str1[i] != '\0' || str2[i] != '\0') {
 if (str1[i] != str2[i]) {
 flag = 1;
 break;
 }
 i++;
 }

 if (flag == 0 && str1[i] == '\0' && str2[i] == '\0')
 printf("Strings are equal");
 else
 printf("Strings are not equal");

 return 0;
}

String Concatenation (Without strcat)

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

int main() {
 char str1[100] = "Hello, ";
 char str2[] = "World!";
 int i, j;

 for (i = 0; str1[i] != '\0'; i++);

 for (j = 0; str2[j] != '\0'; j++) {
 str1[i] = str2[j];
 i++;
 }
 str1[i] = '\0';

 printf("%s\n", str1);
 return 0;
}

Copying Strings

#include <stdio.h>

int main() {
 char source[] = "Hello!";
 char destination[10];
 int i = 0;

 while (source[i] != '\0') {
 destination[i] = source[i];
 i++;
 }
 destination[i] = '\0';

 printf("Copied string: %s\n", destination);
 return 0;
}

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String Length (No strlen)

#include <stdio.h>

int main() {
 char str[] = "Hello";
 int length = 0;
 while (str[length] != '\0') {
 length++;
 }
 printf("Length: %d\n", length);
 return 0;
}

Input and Print a String

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

int main() {
 char str[100];
 printf("Enter a string: ");
 fgets(str, sizeof(str), stdin);
 str[strcspn(str, "\n")] = 0;
 printf("You entered: %s\n", str);
 return 0;
}

Spiral Matrix Traversal

#include <stdio.h>

int main() {
    int rows, cols, i, j;
    scanf("%d %d", &rows, &cols);
    int matrix[rows][cols];
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            scanf("%d", &matrix[i][j]);
        }
    }
    int top = 0, bottom = rows - 1, left = 0, right = cols - 1, dir = 0;
    while (top <= bottom && left <= right) {
        if (dir == 0) {
            for (i = left; i <= right; i++) {
                printf("%d ", matrix[top][i]);
            }
            top++;
        } else if (dir == 1) {
            for (i = top; i <= bottom; i++) {
                printf("%d ", matrix[i][right]);
            }
            right--;
        } else if (dir == 2) {
            for (i = right; i >= left; i--) {
                printf("%d ", matrix[bottom][i]);
            }
            bottom--;
        } else if (dir == 3) {
            for (i = bottom; i >= top; i--) {
                printf("%d ", matrix[i][left]);
            }
            left++;
        }
        dir = (dir + 1) % 4;
    }
    printf("\n");
    return 0;
}

Print Boundary Elements of a Matrix

#include <stdio.h>

int main() {
    int rows, cols, i, j;
    printf("Enter the number of rows: ");
    scanf("%d", &rows);
    printf("Enter the number of columns: ");
    scanf("%d", &cols);

    int matrix[rows][cols];

    printf("Enter the elements of the matrix:\n");
    for (i = 0; i < rows; i++)
        for (j = 0; j < cols; j++)
            scanf("%d", &matrix[i][j]);

    printf("Boundary elements are:\n");
    for (i = 0; i < rows; i++) {
        for (j = 0; j < cols; j++) {
            if (i == 0 || i == rows - 1 || j == 0 || j == cols - 1)
                printf("%d ", matrix[i][j]);
            else
                printf("  ");
        }
        printf("\n");
    }

    return 0;
}

Print Lower Triangle of a Matrix

#include <stdio.h>

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

  for (int i = 0; i < rows; i++) {
    for (int j = 0; j < cols; j++) {
      if (j <= i) {
        printf("%d ", matrix[i][j]);
      } else {
        printf("  ");
      }
    }
    printf("\n");
  }

  return 0;
}

Print Upper Triangle of a Matrix

#include <stdio.h>

int main() {
  int rows, cols, matrix[10][10], i, j;

  printf("Enter the number of rows: ");
  scanf("%d", &rows);
  printf("Enter the number of columns: ");
  scanf("%d", &cols);

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

  printf("Upper triangle of the matrix:\n");
  for (i = 0; i < rows; i++) {
    for (j = 0; j < cols; j++) {
      if (j >= i) {
        printf("%d ", matrix[i][j]);
      } else {
        printf("  ");
      }
    }
    printf("\n");
  }

  return 0;
}

Diagonal Sum of a Square Matrix

#include <stdio.h>

int main() {
 int matrix[10][10];
 int rows, cols, i, j, sum = 0;

 printf("Enter the number of rows (and columns): ");
 scanf("%d", &rows);
 cols = rows;

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

 for (i = 0; i < rows; i++) {
 sum += matrix[i][i];
 }

 printf("Diagonal sum: %d\n", sum);

 return 0;
}

Identity Matrix Checker

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

bool isIdentityMatrix(int matrix[][100], int rows, int cols) {
    if (rows != cols) return false;
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (i == j && matrix[i][j] != 1) return false;
            if (i != j && matrix[i][j] != 0) return false;
        }
    }
    return true;
}

int main() {
    int rows, cols;
    int matrix[100][100];

    printf("Enter rows and columns: ");
    scanf("%d %d", &rows, &cols);

    printf("Enter matrix elements:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            scanf("%d", &matrix[i][j]);
        }
    }

    if (isIdentityMatrix(matrix, rows, cols)) {
        printf("The matrix is an identity matrix.\n");
    } else {
        printf("The matrix is not an identity matrix.\n");
    }

    return 0;
}

Symmetric Matrix Checker

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

bool isSymmetric(int matrix[][100], int rows, int cols) {
    if (rows != cols) {
        return false;
    }
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            if (matrix[i][j] != matrix[j][i]) {
                return false;
            }
        }
    }
    return true;
}

int main() {
    int rows, cols;
    int matrix[100][100];

    printf("Enter the number of rows: ");
    scanf("%d", &rows);
    printf("Enter the number of columns: ");
    scanf("%d", &cols);

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

    if (isSymmetric(matrix, rows, cols)) {
        printf("The matrix is symmetric.\n");
    } else {
        printf("The matrix is not symmetric.\n");
    }

    return 0;
}

Transpose of a Matrix

#include <stdio.h>

int main() {
    int matrix[10][10], transpose[10][10];
    int row, col;
    scanf("%d %d", &row, &col);
    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            scanf("%d", &matrix[i][j]);
        }
    }
    for (int i = 0; i < row; i++) {
        for (int j = 0; j < col; j++) {
            transpose[j][i] = matrix[i][j];
        }
    }
    for (int i = 0; i < col; i++) {
        for (int j = 0; j < row; j++) {
            printf("%d ", transpose[i][j]);
        }
        printf("\n");
    }
    return 0;
}

Matrix Multiplication

#include <stdio.h>

int main() {
    int a[3][3] = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
    int b[3][3] = {{9, 8, 7}, {6, 5, 4}, {3, 2, 1}};
    int result[3][3] = {{0, 0, 0}, {0, 0, 0}, {0, 0, 0}};

    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            for (int k = 0; k < 3; k++) {
                result[i][j] += a[i][k] * b[k][j];
            }
        }
    }

    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", result[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Matrix Subtraction

#include <stdio.h>

int main() {
    int rows, cols;
    printf("Enter rows and columns: ");
    scanf("%d %d", &rows, &cols);

    int matrix1[rows][cols], matrix2[rows][cols], result[rows][cols];

    printf("Enter elements of matrix 1:\n");
    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            scanf("%d", &matrix1[i][j]);

    printf("Enter elements of matrix 2:\n");
    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            scanf("%d", &matrix2[i][j]);

    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            result[i][j] = matrix1[i][j] - matrix2[i][j];

    printf("Resultant matrix:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++)
            printf("%d ", result[i][j]);
        printf("\n");
    }

    return 0;
}

Matrix Addition

#include <stdio.h>

int main() {
    int rows, cols;
    printf("Enter rows and columns: ");
    scanf("%d %d", &rows, &cols);

    int matrix1[rows][cols], matrix2[rows][cols], sum[rows][cols];

    printf("Enter elements of first matrix:\n");
    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            scanf("%d", &matrix1[i][j]);

    printf("Enter elements of second matrix:\n");
    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            scanf("%d", &matrix2[i][j]);

    for (int i = 0; i < rows; i++)
        for (int j = 0; j < cols; j++)
            sum[i][j] = matrix1[i][j] + matrix2[i][j];

    printf("Sum of matrices:\n");
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++)
            printf("%d ", sum[i][j]);
        printf("\n");
    }

    return 0;
}