String Substring

#include <stdio.h>
#include<string.h>
int main(){
	char s1[100];
	char s2[100];
	char *ptr;
	puts("Enter string1");
	gets(s1);
	puts("Enter string2");
	gets(s2);
	ptr = strstr(s1,s2);
	if(ptr == NULL){
	    puts("string not present");
	}
	else{
	    printf("string present at %d",ptr-s1);
	}
	return 0;
}

Enter string1
Hello welcome
Enter string2
wel
string present at 6

#include<stdio.h>
#include<string.h>
int main() 
{
    char s[10] ="123456789";
   char ch = 'Z';
    puts("string before setting");
    puts(s);
   strset(s,ch);
   puts("string after setting");
    puts(s);
   return 0;
}

string before setting
123456789
string after setting
ZZZZZZZZZ