做乘法是调用了加法的运算。编译可以通过，但是输出的答案是奇怪的数字或符号~~~~
没几天就要交了~大家帮帮忙~谢谢！
#include<iostream>
#include<string>
using namespace std;



int Max(int x, int y)
{
    if(x>y)
        return x;
    else return y;}



    int compare(string A,string B)
{
    int lenA,lenB;
    int dxd=0;

    lenA=A.length();
    lenB=B.length();
    if(lenA>lenB)
        dxd=1;
    if(lenA<lenB)
        dxd= -1;
    if(lenA==lenB)
    {
        if(A>B)
            dxd= 1;
        if(A<B)
            dxd=-1;
        if(A==B)
            dxd=0;}
    return dxd;}



string Add(string a,string b)
{
    int lena,lenb,round,i,j;  
    int numa[50]={0},numb[50]={0},sum[50]={0},sumrev[50]={0},carry[50]={0};
    string result=" ";
    lena=a.length();
    lenb=b.length();
    round=Max(lena,lenb);
    for(i=0;i<lena;i++)
        numa[i]=a[lena-1-i]-48;
    for(i=0;i<lenb;i++)
        numb[i]=b[lenb-1-i]-48;
    for(i=0;i<round;i++)
    {
        sum[i]=carry[i]+numa[i]+numb[i];
        if(sum[i]>10)
        {carry[i+1]=1;
        sum[i]=sum[i]-10;}}
    j=0;//j为sum[1024]中经过计算的元素个数
    if(carry[round]=1)
        j=round;
    else j=round-1;
    

    for(i=0;i<50;i++)
    {sumrev[i]=(sum[49-i]+48);}
  
    for(i=50-j;i<50;i++)
    {result=result+char(sumrev[i]);}
    
    return result;
}





int main()
{
    int num[50]={0};

    int lena,lenb,i,j,k;   

    string mula,mulb;
    string sum=" ";
    string pro=" ";
    cout<<"请输入两个数"<<endl;
    cin>>mula>>mulb;
    lena=mula.length();
    lenb=mulb.length();
   
    if(compare(mula,mulb)>=0)
    {
     for(i=0;i<lenb;i++)
        num[i]=mulb[lenb-1-i]-48;}

    if(compare(mula,mulb)==-1)
    {for(i=0;i<lena;i++)
    num[i]=mula[lena-1-i]-48;}
    
    for(i=0;i<lenb;i++)
    {
     for(j=0;j<num[i];j++)
         sum=Add(sum,mula);
     for(k=0;k<i;k++)
     {
         sum=sum+"0";}
         pro=Add(sum,pro);
    }
    cout<<pro<<endl;
        return 0;}

学习中。。。

我的代码:
#include <iostream>
#include <string>


#define MAX  5*25
using namespace std;

int resultBuf[MAX];
int tempBuf[MAX];
int pt[5];

//
void getInfo(const string &str, int &len, int &ptNum){
    
    int sz = str.size();
    len = 0, ptNum = 0;

    for(int iiidx=0; iiidx<sz; ++iiidx){
        if(str[iiidx] == '.')
            ptNum = sz-(iiidx+1);
    }

    int tail = sz-1;
    int num = 0;
    if(ptNum != 0){
        while(str[tail] == '0'){
            --tail;
            ++num;
        }
    }
    ptNum -= num;

    for(int idx=0; idx<=tail; ++idx){
        if(str[idx]=='0' || str[idx]=='.')
            continue;
        
        for(int iidx=0,j=idx; j<=tail; ++j){
            if(str[j] != '.'){
            pt[iidx] = (int)str[j]-48;
                ++iidx;
                ++len;
            }
        }
        break;
    }
}

//pow >= 2
void update(int data[], int pos, int el){
    
    if(data[pos]+el < 10){
        data[pos] += el;
        return;
    }
    
    int over  = (data[pos]+el)/10;
    data[pos] = (data[pos]+el)%10;
    
    update(data, pos-1, over);
}

//
void multi(int data[], int len, int pow){
    
    for(int i=len-1,j=MAX-1; i>=0; --i,--j)
        tempBuf[j] = data[i];
    
    int bufTail = MAX-1;
    int res   = 0;
    int real  = 0;
    int over  = 0;
    int s = len, tempS = s, m = 0;
    
    while(pow >= 2){
    for(int idx=len-1,k=0; idx>=0; --idx){
            while(s > 0){
    res  = data[idx]*tempBuf[bufTail]+over;
                real = res%10;
                
                over = res/10;
over += (real+resultBuf[bufTail-k])/10;
resultBuf[bufTail-k] = (real+resultBuf[bufTail-k])%10;
                --bufTail;
                --s;
            }
        update(resultBuf, bufTail-k, over);
            over = 0;
            ++k;
            s = tempS;
            bufTail = MAX-1;
        }
        --pow;
        over = 0;

        if(pow >=2 ){
            for(m=0; m<MAX; ++m){
        tempBuf[m]   = resultBuf[m];
        resultBuf[m] = 0;
            }
        }

        for(m=0; m<MAX; ++m){
            if(tempBuf[m] != 0){
                s = MAX-m;
                tempS = s;
                break;
            }
        }
    }
}

//
void output(int ptNum){
    
    int tail = MAX-1;
    if(ptNum != 0){
        while(resultBuf[tail] == 0)
            --tail;
    }

    int front = 0;
    while(resultBuf[front] == 0)
        ++front;

    int zeroNum = ptNum-(tail-front+1);
    
    if(zeroNum >= 0)
        cout<<".";
    for(int idx=0; idx<zeroNum; ++idx)
        cout<<"0";

    for(int iidx=front; iidx<=tail; ++iidx){
        if(iidx == tail-ptNum+1)
            cout<<".";
        cout<<resultBuf[iidx];
    }
    cout<<endl;
}
void opOne(const string &str){
    int piv=str.size()-1;
    bool flagpt=false;
    int front = 0;
    
    for(int y=0; y<piv; ++y){
        if(str[y] == '0')
            continue;
        front = y;
        break;
    }

    for(int x=0; x<piv; ++x){
        if(str[x] == '.')
            flagpt = true;
    }
    if(flagpt){
        for(int m=piv; m>=0; --m){
            if(str[piv] == '0'){
                --piv;
            if(str[piv] == '.'){
                     --piv;
                break;
                }
            }
        }
    }
    
    for(int k=front; k<=piv; ++k){
        cout<<str[k];
    }
    cout<<endl;
}
//
int main(){
    
    int len=0, ptNum=0, pow=0;
    string str;
    
    while(cin>>str>>pow){
        if(pow == 1){
            opOne(str);
            continue;
        }

        getInfo(str, len, ptNum);
        ptNum = ptNum*pow;
        
        for(int idx=0; idx<MAX; ++idx)
        resultBuf[idx] = tempBuf[idx] = 0;
        
        multi(pt, len, pow);
        output(ptNum);
    }
    return 0;
}