Rút gọn 2 phân số

#include<iostream>
using namespace std;
struct phanso
{
int tu;
int mau;
}p1,p2;
void main()
{
cout<<"**chuong trinh tinh tong 2 phan so**"<<endl;
cout<<"nhap phan so thu nhat: "<<endl;
cout<<"tu: ";cin>>p1.tu;
do
{cout<<"mau: ";cin>>p1.mau;}
while(p1.mau==0);
cout<<"nhap phan so thu hai: "<<endl;
cout<<"tu: ";cin>>p2.tu;
do
{cout<<"mau: ";cin>>p2.mau;}
while(p2.mau==0);
int i,a,b;
a=p1.tu*p2.mau+p2.tu*p1.mau;
b=p1.mau*p2.mau;

if(a%b!=0)
{
if(a>b)
for(i=1;i<b;i++)
if((a%i==0)&&(b%i==0))
{
a=a/i;
b=b/i;
}
else
for(i=1;i<a;i++)
if((a%i==0)&&(b%i==0))
{
a=a/i;
b=b/i;
}
cout<<"tong cua 2 pso: "<<a<<"/"<<b<<endl;
}
else
cout<<"tong cua 2 pso: "<<a/b<<endl;
}