Bull Math（大数乘法）

最新推荐文章于 2021-01-30 20:28:58 发布

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本文介绍了一个简单的程序，用于验证大型整数相乘的结果是否正确。通过手动实现乘法算法，该程序可以处理最多40位的整数，并输出其精确的乘积。

Description

Bulls are so much better at math than the cows. They can multiply huge integers together and get perfectly precise answers ... or so they say. Farmer John wonders if their answers are correct. Help him check the bulls' answers. Read in two positive integers (no more than 40 digits each) and compute their product. Output it as a normal number (with no extra leading zeros).
FJ asks that you do this yourself; don't use a special library function for the multiplication.

Input

* Lines 1..2: Each line contains a single decimal number.

Output

* Line 1: The exact product of the two input lines

Sample Input

11111111111111
1111111111

Sample Output

12345679011110987654321

#include<stdio.h>
#include<string.h>
#define Len 43 //数的最大长度
int first[Len],second[Len],res[2*Len];
char a[Len],b[Len];
int lena,lenb;
void Mul()
{
	memset(res,0,sizeof(res));
	int i,j,carry=0;
	for(i=1;i<=lena;i++)
		for(j=1;j<=lenb;j++)
		{
			res[i+j-1]+=(first[i]*second[j]);
			res[i+j]+=res[i+j-1]/10;
			res[i+j-1]%=10;
		}
		res[i+j]+=res[i+j-1]/10;
		res[i+j-1]%=10;
		for(i=lena+lenb;i>0&&res[i]==0;i--);//去前导0
		for(;i>=1;i--)
			printf("%d",res[i]);
		printf("\n");
}

int main()
{
	//freopen("b.txt","r",stdin);
	while(scanf("%s %s",a,b)==2)
	{
		int i;
		lena=strlen(a),lenb=strlen(b);
		for(i=0;i<lena;i++)
			first[i+1]=a[lena-1-i]-'0';
		for(i=0;i<lenb;i++)
			second[i+1]=b[lenb-1-i]-'0';
		Mul();
	}
	return 0;
}