Seriously Whats wrong with my code Proble code: LASTDIG2

[iamsethi_sof]

include

int main() {
int t;
scanf("%d",&t);
while(t--)
{
signed long long int b,c;
scanf("%llu %llu",&b,&c);
b=b%10;
if((c==0)&& (b!=0)) printf("%d\n",1);
else
{
if((c%4)==0)
printf("%d\n",((int)pow(b,4))%10);
else
printf("%d\n",((int)pow(b,c%4))%10);
}

}
return 0;

}

[cristaloleg_sof]

You are given two integer numbers: the base a (number of digits d, such that 1<=d<=1000)

10^1000 is mush bigger than 10^18. Your variable b cannot store this value properly.