Given two strings A and B, how would you find out if the characters in B were a subset of the characters in A?

#include <stdio .h>  
#include <conio .h>  
  
int isSubset(char \*a, char \*b);  
int main(){  
  
 char str1\[\]="defabc";  
 char str2\[\]="abcfed";  
  
 if(isSubset(str1, str2)==0)  
   printf("\\nYes, characters in B=\[%s\] are a subset of characters in A=\[%s\]\\n",str2,str1);  
 }  
 else  
 {  
   printf("\\nNo, characters in B=\[%s\] are not a subset of characters in A=\[%s\]\\n",str2,str1);  
 }  
 getch();  
 return(0);  
}  
  
// Function to check if characters in "b" are a subset  
// of the characters in "a"  
int isSubset(char \*a, char \*b)  
{  
 int letterPresent\[256\];  
 int i;  
 for(i=0; i<256; i++)  
    letterPresent\[i\]=0;  
   
 for(i=0; a\[i\]!='\\0'; i++)  
    letterPresent\[a\[i\]\]++;  
   
 for(i=0; b\[i\]!='\\0'; i++)  
    if(!letterPresent\[b\[i\]\])  
       return(1);  
 return(0);  
}