I dont kow what's wrong in this code

#include<stdio.h>
#include<string.h>
int main()
{int n;
scanf("%d",&n);
while(n>0)
{char s1[10000],s2[100000],s3[10000];
scanf("%s%s",s1,s2);
int len1=strlen(s1);
int len2=strlen(s2);
// printf("%d\n%d",len1,len2);
int i,j,count1=0;
// printf(“first string\n”);
int k=0;
s3[k]=s1[0];
k++;
if(k>0)
{int h;
for(i=0;i<len1;i++)//abc
//abcdef
{int count=0;
for(h=0;h<k;h++)//
{
if(s1[i]==s3[h])
{
count++;
}

		}
			if(count==0)
		{s3[k]=s1[i];
		k++;
	}
		
	}
	
}

/*for(i=0;i<len1;i++)
{
	printf("%c\n",s1[i]);
}*/

/* printf(“second string char\n”);
for(j=0;j<len2;j++)
{
printf("%c\n",s2[j]);
}*/

for(i=0;i<k+1;i++)
{for(j=0;j<len2;j++)
{
	if(s3[i]==s2[j])
	{
	count1++;
	}
}}
printf("%d\n",count1);
n--;

// printf("\n%s",s3);
}

}

You need to mention the problem for which you wrote this code and little more about your approach. Reading a code with no clue about problem or solution is very tough and time consuming.