s1 is substring of s2 or not code.c

#include<stdio.h>
#include<string.h>
#include<stdbool.h>
bool is_substring(char *check,char *string) ;


int main(void){
    char s1[] = "pqrst";
    char c1[] = "abc";
    if(is_substring(c1,s1))
    printf("'%s' is a substring of '%s'\n",c1,s1);
    else
      printf("'%s' is not a substring of '%s'\n",c1,s1);

    return 0; 

}
bool is_substring(char *check,char *string){
    int slen=strlen(string);
     int clen=strlen(check);
     int end = slen-clen+1;
     for(int i=0;i<end;i++){
         bool check_found=true;
         for(int j=0;j<clen;j++){
            if(check[j]!=string[i+j]){
                check_found=false;
                break;
            }
         }
         if(check_found) return true;

     }
     return false;

}