分数运算

题目：https://www.nowcoder.com/pat/2/problem/261

#include <cstdio>
#include <algorithm>
#include <cmath>
using namespace std;
#define max(x,y) x>y?x:y
#define min(x,y) x<y?x:y

int main(){
    int a, b, c, d;
    char ch;
    while (scanf("%d/%d %d/%d %c",&a,&b,&c,&d,&ch) != EOF){
        if (ch == '+'){
            a = a*d + c*b;
            b = b*d;
        }
        else if (ch == '-'){
            a = a*d - c*b;
            b = b*d;
        }
        else if (ch == '*'){
            a = a*c;
            b = b*d;
        }
        else if (ch == '/'){
            int t = c;
            c = d;
            d = t;    
            a = a*c;
            b = b*d;
        }

        int a1 = 1;
        int b1 = 1;
        if (a < 0)
            a1 = 0;
        if (b < 0)
            b1 = 0;
        int c1 = a1 + b1;
        a = abs(a);
        b = abs(b);
        c = max(a, b);    //被除数
        d = min(a, b);    //除数
        while (d){
            int t = c / d;
            int v = c%d;
            c = d;
            d = v;
        }
        if (c1 == 1){
            printf("-");
        }
        printf("%d/%d
", a / c, b / c);
    }
    return 0;
}