Your way of coding is making a easy things to difficult one.Also as shabbir said segmentation fault is not a compile time error . It is a run time error .But when I run I didn't get segmentation fault . I got a unterminated loop.


Code:
    
for( i = 0 ; i <= (x = (strlen(c))) ; i++)
You can write like this ,

Code:
   
 for( i = 0 ; i <= strlen(c); i++)
Also you have used '=' for the comparison.You need to use '==' for that.

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

int main()
{
    int i,x;
    char c[100];

    printf("Enter input :");
    fgets(c,100,stdin);

    for( i = 0 ; i <= strlen(c); i++)
    {

        if( c[i] == '\t')
        {
                        printf("****"); // I used '*' for the understanding , you just change it to space .
        }
        else
        {
        printf("%c",c[i]);
        }
    }
}