大数乘法

大数乘法c版(基础写法)

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#include<stdio.h>
#include<string.h>
#define N 202

int main() {
int a[N] = {0}, b[N] = {0}, c[404] = {0}, la, lb, i, j,k, d = 0, n1, n2;//202位数相乘,最长404位数
int get(int *p);
void change(int *a, int *b, int n);

la = get(a);
lb = get(b);
n1 = la > lb ? la : lb;//较长的数长
n2 = la < lb ? la : lb;//较短的数长

if (la < lb)
change(a, b, lb);

//模拟乘法运算过程(进位等考虑)
for (i = 0; i < n2; i++) {
for (j = 0; j < n1; j++) {
c[j + i] += (b[i] * a[j] + d)%10;
d = (b[i] * a[j] + d) / 10;

if (c[j+i]>9){
d++;
c[j+i]%=10;
}
if (a[j+1]==0&&d!=0){
k=j+i+1;
c[k]=d;
}
}
d=0;
}

k=k>(j+i-2)?k:j+i-2;
for (i = k; i >= 0; i--)//将倒序装入的结果打印
printf("%d", c[i]);

return 0;
}

//输入字符串作为数字,并返回数字去除前导0后的长度
int get(int *p) {
char x[N];
int l, i, ex = 0;

scanf("%s", x);
l = strlen(x);
while (x[ex] == '0')
ex++;
for (i = ex; i < l; i++) //提取字符串数字到int数组,倒序排列
*(p + l - i - 1) = x[i] - '0';
return l - ex;
}


void change(int *a, int *b, int n) {
int i, t;
for (i = 0; i < n; i++) {
t = a[i];
a[i] = b[i];
b[i] = t;
}
}

程序运行结果

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1234567890123456789
98765432109876543210
121932631124517831023715309991126352690

感谢支持 !
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