Custom Struct-returning function stuck on input?

Question

I wanted to make a function with structs to simplify rational numbers ,
one member is the numerator(int) and the other is the denominator(int) but the program stucks at input!! I am aware that scanf() is a bit risky but I thought its just a couple of integers!

#include <stdio.h>
#include <stdlib.h>

typedef struct rational{
    int num;
    int den;
}rational;

rational makerational(int num,int den);
void printrational(rational r);
int main()
{
    int a,b;
    printf("\n\n Input integers for fraction:");
    scanf(" %d%d",&a,&b);
    printrational(makerational(a,b));
}
rational makerational(int a,int b){
    int live=1; 
    rational r;
    r.num=a;
    r.den=b;
  while(live){  
    if(!(r.num%2 && r.den%2)){
        r.num/=2;
        r.den/=2;
    }else if(!(r.num%3 && r.den%3)){
        r.num/=3;
        r.den/=3;
    }else if(!(r.num%5 && r.den%5)){
        r.num/=5;
        r.den/=5;
    }else if(!(r.num%7 && r.den%7)){
        r.num/=7;
        r.den/=7;
    }else live--;
  }
    return r;
}
void printrational(rational r){
    printf("\nFRACTION -> %d/%d\n",r.num,r.den);
}

Answer 1

You getting stuck in an infinite loop here:

while(live){  
    if(!(r.num%2 && r.den%2)){
        r.num/=2;
        r.den/=2;
    }

    …
}

For example, when r.num == 1 and r.den == 2, consider what's happening:

Iteration 1

r.num % 2 == 1 % 2 == 1
r.den % 2 == 2 % 2 == 0
!(1 && 0) == 1

r.num / 2 == 1 / 2 == 0
r.den / 2 == 2 / 2 == 1

Iteration 2

r.num % 2 == 0 % 2 == 0
r.den % 2 == 1 % 2 == 1
!(0 && 1) == 1

r.num / 2 == 0 / 2 == 0
r.den / 2 == 1 / 2 == 0

Iteration 3 to infinity and beyond…

r.num % 2 == 0 % 2 == 0
r.den % 2 == 0 % 2 == 0
!(0 && 0) == 1

r.num / 2 == 0 / 2 == 0
r.den / 2 == 0 / 2 == 0

Change the expressions in the branching statements to something like this to correct your logic:

while(live)
{
    if((r.num % 2 == 0) && (r.den % 2 == 0))
    {
        r.num /= 2;
        r.den /= 2;
    }

    …
}

Answer 2

Problem is, when you enter 8 20, numbers change like fallowing;

4 10

2 5

1 2

0 1

0 0 <--- here is the infinite loop

reason is, integer rounds down the number, you should add a control statement for the case that numbers reach 0