样例输入
1/8+3/8
1/4-1/2
1/3-1/3
样例输出
1/2
-1/4
0

#include <stdio.h>
#include <math.h>
int fun(int m,int n)
{   
    int r;
    if(m<n){r=m;m=n;n=r;}
    while(n!=0){r=m%n;m=n;n=r;}
    return m;  
}
void main()
{
        int a1,a2,b1,b2,c1,c2,t,i;  char ch;
        
    printf("分数计算，输入格式形如：1/8+3/8 1/4-1/2\n");
        scanf("%d/%d%c%d/%d",&a1,&a2,&ch,&b1,&b2);

    t=fun(a2,b2);   
    c2=a2*b2/t;

        if(ch=='-')b1=-b1;
    c1=a1*b2/t+b1*a2/t;

    for(i=2; i<=abs(c1) && i<=c2;i++)     //最简约
        if(c1%i==0 && c2%i==0){ c1/=i; c2/=i;}

    if(c1==0 || c2==1)printf("%d\n",c1);
    else printf("%d/%d\n",c1,c2);
}

去看这个帖
https://bbs.bccn.net/viewthread.php?tid=337049&page=1#pid1942288

路过、、

void f(int m,int n)
{int i;
if(m==0)
printf("0");
else if(m==n)
printf("1");
else
{
for(i=m>n?m:n;i>0;i--)
if(m%i==0&&n%i==0)
break;
if(m%n==0)
printf("%d",m/n);
else if(n%m==0)
printf("1/%d",n/m);
else
printf("%d/%d",m/i,n/i);
}}
main()
{int a1,a2,b1,b2,i=1;
char c;
scanf("%d/%d%c%d/%d",&a1,&a2,&c,&b1,&b2);
while(1)
{if(i%a2==0&&i%b2==0)
break;
else i++;}
a1=a1*i/a2;
b1=b1*i/b2;
switch(c)
{case '+':f(a1+b1,i);break;
case '-':f(a1-b1,i);break;}getch();
}