大数相乘

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改变 op1 和 op2 可以实现任意位数的计算，代码如下：

#include<stdio.h>#include<stdlib.h>#include<string.h>void calc(char *op1,char *op2){int i;int j;int k = 0;int re;int carry = 0;int op1_len = strlen(op1);         //5int op2_len = strlen(op2);//5char *result = (char *)malloc(op1_len + op2_len + 1);for(i = 0;i <= op1_len + op2_len;i++)result[i] = 0;for(i = op1_len - 1;i >= 0;i--){for(carry = 0,j = op2_len - 1;j >= 0;j--){re = (op1[i] - '0') * (op2[j] - '0') + result[i + j + 1] + carry;result[i + j + 1] = (char)(re % 10);carry = (char)(re / 10);}//for(i = 0;i < op1_len + op2_len;i++)//printf("%d",result[i]);//printf("\n");result[i] = (char)carry;}for(i = 0;result[i] == 0 && i < op1_len + op2_len;i++);for(;i < op1_len + op2_len;i++)printf("%d",result[i]);}int main(){char *op1 = "1234567891011121314151617181920";char *op2 = "2019181716151413121110987654321";//char *op1 = "10000";//char *op2 = "10000";char *op3 = "12345";//  152399025//char *op1 = "99999";//char *op2 = "99999";// 9999800001char *op4 = "54321";// 2950771041calc(op1,op2);return 0;}