Lab: Advanced String Operations

1. Program to Remove All Duplicate Characters from a String

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

int main() {
  char str[100], result[100] = {0};
  int flag[256] = {0}; // ASCII characters table
  int j = 0;

  printf("Enter a string: ");
  scanf("%[^\n]s", str);

  for (int i = 0; str[i] != '\0'; i++) {
    if (flag[(unsigned char)str[i]] == 0) {
      result[j++] = str[i];
      flag[(unsigned char)str[i]] = 1;
    }
  }
  result[j] = '\0'; // Null terminate the result string

  printf("String after removing duplicates: %s\n", result);

  return 0;
}

2. Program to Count the Occurrences of a Substring in a Given String

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

int main() {
  char str[100], subStr[50];
  int count = 0;
  char *pos;

  printf("Enter the main string: ");
  scanf("%[^\n]s", str);
  getchar(); // Clear the buffer
  printf("Enter the substring: ");
  scanf("%[^\n]s", subStr);

  pos = strstr(str, subStr);
  while (pos != NULL) {
    count++;
    pos = strstr(pos + 1, subStr);
  }

  printf("Occurrences of '%s': %d\n", subStr, count);

  return 0;
}

3. Program to Replace a Substring in a String with Another Substring

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

void replaceSubstring(char *str, char *subStr, char *replaceStr) {
  char result[200] = {0}; // Buffer to store result
  char *pos, *start = str;
  int lenSub = strlen(subStr);

  while ((pos = strstr(start, subStr)) != NULL) {
    // Append part before the substring
    strncat(result, start, pos - start);
    // Append the replacement substring
    strcat(result, replaceStr);
    // Move start pointer beyond the found substring
    start = pos + lenSub;
  }
  // Append remaining part of the original string
  strcat(result, start);

  printf("String after replacement: %s\n", result);
}

int main() {
  char str[100], subStr[50], replaceStr[50];

  printf("Enter the main string: ");
  scanf("%[^\n]s", str);
  getchar(); // Clear the buffer
  printf("Enter the substring to replace: ");
  scanf("%[^\n]s", subStr);
  getchar(); // Clear the buffer
  printf("Enter the replacement substring: ");
  scanf("%[^\n]s", replaceStr);

  replaceSubstring(str, subStr, replaceStr);

  return 0;
}

4. Program to Find Digits and Add Them Up in a String

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

int main() {
  char str[100];
  int sum = 0;

  printf("Enter a string: ");
  scanf("%[^\n]s", str);

  for (int i = 0; str[i] != '\0'; i++) {
    if (isdigit(str[i])) {
      sum += str[i] - '0';
    }
  }

  printf("Sum of digits in the string: %d\n", sum);

  return 0;
}