程序要求输入两个整形变量，分别是分子（Numerator）和分母（Denominator），通过void enter(struct Fraction *fraction); void simplify(struct Fraction *fraction); void display(struct Fraction fraction);这三个函数实现输入，简化（2/8变成1/4）和输出。本人调试了很久都只输出原来输入的结果。比如2,8（结果是2/8），4, -16(应该是-1/4, 输出结果是4/-16)。 下面是三个文件（无需main.h即可编译），请大家指点一下，谢谢。
// w2.cpp
 #include <iostream>
 using namespace std;
 #include "Fraction.h"

 int main() {
     struct Fraction fraction;

     cout << "Fraction Simplifier" << endl;
     cout << "===================" << endl;

     enter(&fraction);
     simplify(&fraction);
     display(fraction);
 }

//Fraction.h
struct Fraction{
 int num;
 int den;
};

void enter(struct Fraction *fraction);
void simplify(struct Fraction *fraction);
void display(struct Fraction fraction);

//Fraction.cpp
#include <iostream>
using namespace std;
#include "Fraction.h"
void enter(struct Fraction *fraction)
    {
    cout << "Numerator: "<< endl;
    cin>>fraction->num;
    cout << "Denominator: "<< endl;
    cin>>fraction->den;
    if (fraction->den==0)
      {
       cout << "Denominator (not zero): "<< endl;
       cin>>fraction->den;
       }
    }

void simplify(struct Fraction* fraction)
    {
    int i;   
    if ((fraction->num>0 && fraction->den>0) || (fraction->num>0 && fraction->den<0)) //ex. 2/4 or 2/-4
    {
     for (i=fraction->num; i>0; i--)
       {
        if (fraction->den>0)
        {
        if (fraction->num%i==0 && fraction->den%i==0)
            {
            fraction->num==fraction->num/i;
            fraction->den==fraction->den/i;
            }
        }
        else
           {
               if (fraction->num%i==0 && fraction->den%i==0)
                  {
                   fraction->num==-1*(fraction->num/i);
                   fraction->den==-1*(fraction->den/i);
                  }
           }
       }
     }
     else if ((fraction->num<0 && fraction->den>0) || (fraction->num<0 && fraction->den<0))//ex. -2/4 or -2/-4
     {
       for (i=fraction->num; i<0; i++)
       {
        if (fraction->den<0)
        {
           if (fraction->num%i==0 && fraction->den%i==0)
              {
               fraction->num==fraction->num/i;
               fraction->den==fraction->den/i;
               }
         }
        else
         {
            if (fraction->num%i==0 && fraction->den%i==0)
               {
                fraction->num==-1*(fraction->num/i);
                fraction->den==-1*(fraction->den/i);
                }
         }
        }   
      }
    }

void display(struct Fraction fraction)
    {
    cout<<endl;
    if (fraction.num==0)
        cout<<"0"<<endl;
    else
        cout<<fraction.num<<"/"<<fraction.den<<endl;
    }

用visual studio， 没警告。我自己修好了。谢谢。