大数减法

大数减法模板只支持正数的大数减法并且被减数大于减数

#include <iostream>
#include <cstdlib>
#include <cstring>
#include <string>
using namespace std;

#define MAXN 100

char* Subtraction(string A, string B);

int main()
{
    string num1, num2;
    cin>>num1>>num2;
    Subtraction(num1, num2);

    return 0;
}

char* Subtraction(string A, string B)
{
    int i,k;
    int len1, len2;
    int up;
    int length;

    len1 = A.length();
    len2 = B.length();
    int a[MAXN+4] ={0};
    int b[MAXN+4] ={0};
    int c[MAXN+4] ={0};

    for(k=0,i=len1-1; i>=0; i--)
        a[k++] = A[i]-'0';
    for(k=0,i=len2-1; i>=0; i--)
        b[k++] = B[i]-'0';

    for(i=0,up=0; i<MAXN; i++)
    {
        c[i] = a[i]-b[i]-up;
        if(c[i]<0)
        {
            c[i] += 10;
            up=1;
        }
        else up = 0;
    }
    for(i=MAXN; i>=0; i--)
        if(c[i]) break;
    length = i+1;
    cout<<length<<endl;

    char* result = (char *)malloc((sizeof(char)*length));
    for(i=length-1,k=0; i>=0; i--)
        result[k++] = c[i]+ '0';

    //测试输出
    cout<<A<<" - "<<B<<" = ";
    for(i=0; i<length; i++)
        cout<<result[i];
    cout<<endl;

    return result;
}