Last digit Re Visited(LASTDIG2)

LASTDIG2

#include<stdio.h>
#include<string.h>
int main()
{
char str[1005];
unsigned long long int b,a,ans,len,t;
scanf("%llu",&t);
while(t--){
scanf("%s",str);
scanf("%llu",&b);
 len=strlen(str);
a=str[len-1]-'0';
if(b==0&&a!=0) ans=1;
else{
if(a==0){ ans=0; goto end;}
if(a==5) {ans=5; goto end;}
switch(b%4){
case 0: ans=a%2!=0? 1:6;
break;
case 1: ans=a;
break;
case 2: ans=a*a%10;
break;
default : ans=a*a*a%10;
break;
}
}
end :
printf("%llu\n",ans);
}
return 0;
}