POJ 2389 Bull Math

#include <iostream>
#include <cstdio>
#include <cstring>
#define REP(i, s, n) for(int i = s; i <= n; i ++)
#define REP_(i, s, n) for(int i = n; i >= s; i --)
#define MAX_N 2000

using namespace std;

char a[MAX_N], b[MAX_N];
int la, lb, lc;
int int_a[MAX_N], int_b[MAX_N], int_c[MAX_N];

int main(){
    scanf("%s%s", a + 1, b + 1);
    la = strlen(a + 1); lb = strlen(b + 1);
    memset(int_a, 0, sizeof(int_a)); memset(int_b, 0, sizeof(int_b));
    memset(int_c, 0, sizeof(int_c));
    REP(i, 1, la) int_a[la - i + 1] = a[i] - ‘0‘;
    REP(i, 1, lb) int_b[lb - i + 1] = b[i] - ‘0‘;
    REP(i, 1, la){
        int x = 0;
        REP(j, 1, lb){
            int_c[i + j - 1] = int_a[i] * int_b[j] + x + int_c[i + j - 1];
            x = int_c[i + j - 1] / 10; int_c[i + j - 1] %= 10;
        }
        int_c[i + lb] = x;
    }
    lc = la + lb;
    while(int_c[lc] == 0 && lc > 1) lc--;
    REP_(i, 1, lc) printf("%d", int_c[i]);
    return 0;
}