多位整数乘法

//============================================================================

// Name : multiply.cpp

// Author : Rick

// Version :

// Copyright : Your copyright notice

// Description : Hello World in C++, Ansi-style

//============================================================================


#include <iostream>
#include <stdlib.h>
#define MAXLEN 1023

using namespace std;

int strlen(const char *str);
void add(char *num1, char *num2, char *add);
void strcpy(char *str1, char *str2);
void reverse(char *str);
int multipy(char *num1, char *num2, char *mul);
void multipy(char *num, int n, int *mul);
void strshift(char *str, int shift);

int main() {


    char *s=new char[MAXLEN*2+1];
    char *n=new char[MAXLEN*2+1];

    cout<<"input you factor s: ";
    cin>>s;
    cout<<"input you factor n: ";
    cin>>n;

    char *mul =new char[MAXLEN*2+1] ;
    mul[0]='\0';
    int bit=multipy(s, n, mul);
    cout << "Multiply " << s << " * " << n << " = " << mul << endl;
    cout<<"bits: "<<bit<<endl;
    delete []mul;
    delete []s;
    delete []n;

    system("pause");
    return 0;
}

int strlen(const char *str) {
    int len = 0;
    const char *p = str;
    while (*p++ != '\0') {
        len++;
    }
    return len;
}

void add(char *num1, char *num2, char *add) {
    int carry = 0;
    int len = 0;
    int len1 = strlen(num1);
    int len2 = strlen(num2);
    bool iscarry;
    int sum;
    char *temp = new char[MAXLEN * 2 + 1];

    while (len1 > 0 && len2 > 0) {
        len1--;
        len2--;

        sum = carry + num1[len1] + num2[len2] - '0' - '0';
        iscarry = (sum >= 10);

        temp[len++] = iscarry ? sum % 10 + '0' : sum + '0';
        carry = iscarry ? sum / 10 : 0;

    }
    while (len1 > 0) {
        len1--;
        sum = carry + num1[len1] - '0';
        iscarry = (sum >= 10);

        temp[len++] = iscarry ? sum % 10 + '0' : sum + '0';
        carry = iscarry ? sum / 10 : 0;

    }
    while (len2 > 0) {
        len2--;
        sum = carry + num2[len2] - '0';
        iscarry = (sum >= 10);

        temp[len++] = iscarry ? sum % 10 + '0' : sum + '0';
        carry = iscarry ? sum / 10 : 0;

    }
    if (carry)
        temp[len++] = carry + '0';
    temp[len] = '\0';
    reverse(temp);
    strcpy(add, temp);

    delete[] temp;
}
void multipy(char *num, int n, char *mul) {
    int lenNum = strlen(num);
    int len = 0;
    int carry = 0;
    char *temp = new char[MAXLEN * 2 + 1];
    while (--lenNum >= 0) {
        temp[len++] = (num[lenNum] - '0') * n + carry >= 10 ? ((num[lenNum]
                - '0') * n + carry) % 10 + '0' : (num[lenNum] - '0') * n
                + carry + '0';
        carry = (num[lenNum] - '0') * n + carry >= 10 ? ((num[lenNum] - '0')
                * n + carry) / 10 : 0;

    }
    if (carry)
        temp[len++] = carry + '0';
    temp[len] = '\0';
    reverse(temp);
    strcpy(mul, temp);

    delete[] temp;
}
int multipy(char *num1, char *num2, char *mul) {
    char *n1;
    char *n2;
    char *temp;
    char *sum;
    int len1;
    int len2;
    temp = new char[MAXLEN * 2 + 1];
    sum = new char[MAXLEN * 2 + 1];
    temp[0] = '0';
    temp[1] = '\0';
    sum[0] = '0';
    sum[1] = '\0';
    n1 = new char[MAXLEN * 2 + 1];
    n2 = new char[MAXLEN * 2 + 1];
    len1 = strlen(num1);
    len2 = strlen(num2);
    strcpy(n1, num1);
    strcpy(n2, num2);
    int i = 0;
    int n = 0;
    if (len1 > len2)
        while (--len2 >= 0) {
            n = n2[len2] - '0';
            multipy(n1, n, temp);
            strshift(temp, i++);
            add(sum, temp, sum);
        }
    else
        while (--len1 >= 0) {
            n = n1[len1] - '0';
            multipy(n2, n, temp);
            strshift(temp, i++);
            add(sum, temp, sum);
        }
    strcpy(mul, sum);
    delete[] temp;
    delete[] sum;
    delete[] n1;
    delete[] n2;
    return strlen(mul);

}
void strshift(char *str, int shift) {
    int len = strlen(str);

    for (int i = len; i < len + shift; i++) {
        str[i] = '0';
    }
    str[len + shift] = '\0';

}
void strcpy(char *str1, char *str2) {
    int len2 = strlen(str2);
    int len1 = 0;
    while (len1 <= len2) {
        str1[len1] = str2[len1];
        len1++;
    }
    str1[len1] = '\0';

}
void reverse(char *str) {
    int len = strlen(str);

    char tmp;
    int low = 0, hi = len - 1;
    while (low < hi) {
        tmp = str[hi];
        str[hi] = str[low];
        str[low] = tmp;
        low++;
        hi--;
    }
}