UVA 10405 Longest Common Subsequence

#include<iostream>
#include<cstdio>
#include<string>
#include<cstring>
using namespace std;
int dp[1001][1001];
int MAX(int x,int y)
{
    if (x>y) return x;
    else return y;
}
int main()
{
    char str1[1001],str2[1001];
    int sum;
    while(gets(str1)!=NULL)
    {
        gets(str2);
        memset(dp,0,sizeof(dp));
        int len1,len2;
        len1=strlen(str1);
        len2=strlen(str2);
        for (int i=1;i<=len1;i++)
            for (int j=1;j<=len2;j++)
            {
                if (str1[i-1]==str2[j-1]) sum=1;
                else sum=0;
                dp[i][j]=MAX(dp[i-1][j],MAX(dp[i][j-1],dp[i-1][j-1]+sum));
            }
        cout<<dp[len1][len2]<<endl;
    }
    return 0;
}