How to replace two chars with one char?

Question

So I'm trying to replace cc with & in a sentence (eg: "Hi this is Mark cc Alice"). So far I have this code where it replaces the first c with & but the second c is still there. How would I get rid of the second c?

int main() {
    char str[] = "Hi this is Mark cc Alice";
    int i = 0;
    while (str[i] != '\0') {
        if (str[i] == 'c' && str[i + 1] == 'c') {
            str[i] = '&';  
            //str[i + 1] = ' ';
        }
        i++;
    }
    printf("\n-------------------------------------");
    printf("\nString After Replacing 'cc' by '&'");
    printf("\n-------------------------------------\n");
    printf("%s\n",str);
    return str;
}

The input is:

Hi this is Mark cc Alice

The Output is:

Hi this is Mark &c Alice

Answer 1

You can just shuffle it over one spot using a generic "move back" function:

void shunt(char* dest, char* src) {
  while (*dest) {
    *dest = *src;
    ++dest;
    ++src;
  }
}

Where you can use it like this:

int main(){
  char str[] = "Hi this is Mark cc Alice";

  for (int i = 0; str[i]; ++i) {
    if (str[i] == 'c' && str[i+1] == 'c') {
      str[i]='&';

      shunt(&str[i+1], &str[i+2]);
    }
  }

  printf("\n-------------------------------------");
  printf("\nString After Replacing 'cc' by '&'");
  printf("\n-------------------------------------\n");
  printf("%s\n",str);

  // main() should return a valid int status code (0 = success)
  return 0;
}

Note the switch from the messy int declaration + while + increment into one for loop. This would be even less messy using a char* pointer instead:

for (char* s = str; *s; ++s) {
  if (s[0] == 'c' && s[1] == 'c'){
    *s = '&';

    shunt(&s[1], &s[2]);
  }
}

When working with C strings it's important to be comfortable working with pointers as that can save you a lot of hassle.

You should also familiarize yourself with the C Standard Library so you can use tools like strstr instead of writing your own equivalent of same. Here strstr(str, "cc") could have helped.

Answer 2

You have to shift the whole array to left. A simple way of doing that is :

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

#define STR_SIZE 25

int main(){
  char str[STR_SIZE] = "Hi this is Mark cc Alice";
  int i=0,j=0;

  while(str[i]!='\0'){
    if(str[i]=='c' && str[i+1]=='c'){ 
      str[i]='&';
      for (j=i+1; j<STR_SIZE-1; j++) /* Shifting the array to the left */
      {
          str[j]=str[j+1];
      }
    }
    i++;
  }
  printf("\n-------------------------------------");
  printf("\nString After Replacing 'cc' by '&'");
  printf("\n-------------------------------------\n");
  printf("%s\n",str);
  return 0;
}