how to find gcd of two numbers in c 2b 2b

1// gcd function definition below:
2int gcd(int a, int b) {
3   if (b == 0)
4   return a;
5   return gcd(b, a % b);
6}
7
8int a = 105, b = 30;
9cout<<"GCD of "<< a <<" and "<< b <<" is "<< gcd(a, b);
10// output = "GCD of 105 and 30 is 15";

1#include<iostream>
2using namespace std;
3long long gcd(long long a, long long b) 
4{ 
5    if (b == 0) 
6        return a; 
7    return gcd(b, a % b);  
8      
9} 
10int main()
11{
12	long long a,b;
13	cin>>a>>b;
14	cout<<gcd(a,b);
15}

1#include<bits/stdc++.h>
2using namespace std;
3long long UCLN(long long a,long long b)
4{
5    long long r;
6    while (b!=0)
7    {
8        r=a%b;
9        a=b;
10        b=r;
11    }
12    return a;
13}
14
15
16int main()
17{
18    long long a, b;
19    cout<< "enter: ";
20    cin>> a;
21    cout<< "enter: ";
22    cin >>b;
23    cout<<UCLN(a,b)<<endl;
24    return 0;
25}