uva 10106 Product （大数相乘）

Product

The Problem

The problem is to multiply two integers X, Y. (0<=X,Y<10250)

The Input

The input will consist of a set of pairs of lines. Each line in pair contains one multiplyer.

The Output

For each input pair of lines the output line should consist one integer the product.

Sample Input

12
12
2
222222222222222222222222

Sample Output

144
444444444444444444444444

题解----数组模拟储存大数的每一位，再相乘，进位。注意 0*123和123*0的特殊情况
#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int a[300],b[300],c[700];
char str_1[300], str_2[300];
int main()
{
int i,p,q,j;
while(cin>>str_1)
{
q=0;
cin>>str_2;
if(strcmp(str_1,"0")==0||strcmp(str_2,"0")==0)
{
printf("0\n");
continue;
}
memset(a,0,sizeof(a));
memset(b,0,sizeof(b));
memset(c,0,sizeof(c));
for(i=strlen(str_1)-1,p=299;i>=0;i--,p--)
a[p]=str_1[i]-'0';
for(i=strlen(str_2)-1,p=299;i>=0;i--,p--)
b[p]=str_2[i]-'0';
for(i=299;i>=0;i--)
{
for(j=299,p=699-(299-i);j>=0;j--,p--)//关键是P的变化，每乘一位P要加1
{
c[p]=c[p]+a[i]*b[j];
}
}
for(i=699;i>=0;i--)
{
c[i-1]=c[i-1]+c[i]/10;
c[i]=c[i]%10;
}
for(i=0;i<700;i++)
{
if(c[i]==0&&q==0)
continue;
else
{
cout<<c[i];
q=1;
}
}
puts("");
}
return 0;
}

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