Why this C code is displaying wrong answer?

Question

//Actually I am solving a beginner Comitative programming problems.
//Question link:
https://codeforces.com/problemset/problem/61/A

//My code:
#include <stdio.h>
#include <stdlib.h>
#include<string.h>
#define S 100
int main()
{
char str1[S];//input string
char str2[S];//input string

int i,j;
scanf(" %s",str1);
scanf(" %s",str2);

const len=strlen(str1);

char str3[len];//output string

for(i=0;i<len;i++)
{

if(str1[i]== str2[i])
{
str3[i]='0';
}

else
{
str3[i]='1';
}
}
printf("%s",str3);
return 0;
}

//Wrong answer on test 3 but it passes the first 2 cases
//01110 //str1
//01100 //str2
//00010‼@ //str3, (wrong answer) it outputs additional character as (!!@)

Answer 1

You can run loop just for len and print inside loop instead of making new string

Answer 2

Ok i will try

Answer 3

Martin Taylor thanks a lot❤️