Problem 1453 Bignum Arithmetic from http://acm.fzu.edu.cn/problem.php?pid=1453

Problem 1453 Bignum Arithmetic

Accept: 399 Submit: 1028

Time Limit: 1000 mSec Memory Limit : 32768 KB

Problem Description

In this problem, you will be concerned with integers with very large numbers of digits. You must write code which will repeatedly accept (until end of file) two lines each containing an unsigned integer, and output the product of the two input unsigned integers.
The output must not contain any leading zeros.

You can assume that each integer will contain at most 80 digits. The input ends with an end of file.

Sample Input

03421298123

Sample Output

44391636

#include <iostream>
#include <cstdio>
#include <string.h>
using namespace std;
int a[100];
int b[100];
char s1[100];
char s2[100];
int c[200];
int lena, lenb, i, j, len;
void multi(){
memset(c, 0, sizeof(c));
len = lena+lenb;

for(i=0;i<lena;++i)
for(j=0;j<lenb;++j){
c[i+j] += a[i]*b[j];
}
for(i=0;i<len;++i){
c[i+1] += c[i]/10;
c[i] %= 10;
}

len++;
while(len>0 && !c[len-1])
len--;

}
int main(){

//freopen("in.txt", "r", stdin);
while(cin>>s1>>s2){
lena = strlen(s1);
lenb = strlen(s2);
for(i=lena-1;i>=0;--i)
a[lena-1-i] = s1[i] - '0';
for(i=lenb-1;i>=0;--i)
b[lenb-1-i] = s2[i] - '0';
multi();
if(len==0)
printf("0");
else
for(i=len-1;i>=0;i--)
cout<<c[i];
printf("\n");
}

//fclose(stdin);
return 0;
}