Question

The following program compiles but has gibberish data inside of it and doesn’t replace..

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

int main (void)
    {
    int i;
    char string[100];
    printf("Enter a string");
    fgets(string, 100, stdin);
    for (i=0; i<strlen(string);i++)
    {
        if (string[i]=='o')
        {
            string[i]='0';

        }

    }
    printf("%c", string);
    return 0;
}

Answer 1

Calculate strlen before loop

Use %s instead of %c

printf("%s", string);

As suggested by Vallabh Patade you don’t need to calculate length:

char *p, string[100];

printf("Enter a string");
p = fgets(string, 100, stdin);
while (*p) {
    if (*p == 'o') *p = '0';
    p++;
}
printf("%s", string);