If you were to generalize this problem, to say "Does a string str end with a string suffix?" you could do the following:

#include <string.h>

int endswith(char* str, char* suffix) 
{
    // assuming that str and suffix are not NULL
    return strcmp(str + strlen(str) - strlen(suffix), suffix) == 0;
}

It would be trivial to add a check for NULL to the function as well:

#include <string.h>

int endswith(char* str, char* suffix) 
{
    return str && suffix && strcmp(str + strlen(str) - strlen(suffix), suffix) == 0;
}