Gcd of two numbers in c

• To check GCD of two numbers first we need to read input from user. i.e ask user to enter two numbers
• Store those two numbers in two integer variables
• Check if number is factor of given two numbers by iterating in for loop.

2. #include <stdio.h>
3. // program to check gcd of two numbers in c 
4. // write a c program to find gcd of two integers
5. // www.instanceofjava.com
6. int main()
7. {
8.     int number1, number2, i, gcd;
9.     // read input from user
10.     printf(" please enter any two numbers: ");
11.     scanf("%d %d", &number1, &number2);
12. 
    
13.     for(i=1; i <= number1 && i <= number2; ++i)
14.     {
15.         // checking  if i is divisible by both numbers / factor of both numbers
16.         if(number1%i==0 && number2%i==0)
17.             gcd = i;
18.     }
19. 
    
20.     printf("GCD of %d and %d is %d", number1, number2, gcd);
21. 
    
22.     getch();
23. }

Output:

2. 
   
3. #include <stdio.h>
4. // Function to compute Greatest Common Divisor using Euclidean Algorithm
5. int gcd(int a, int b) {
6.     while (b != 0) {
7.         int temp = b;
8.         b = a % b;
9.         a = temp;
10.     }
11.     return a;
12. }
13. 
    
14. int main() {
15.     int num1, num2;
16. 
    
17.     // enter  two numbers from the user
18.     printf("Enter two numbers to find their GCD: ");
19.     scanf("%d %d", &num1, &num2);
20. 
    
21.     // Ensure numbers are positive
22.     if (num1 < 0) num1 = -num1;
23.     if (num2 < 0) num2 = -num2;
24. 
    
25.     // Calculate and display the GCD
26.     int result = gcd(num1, num2);
27.     printf("The GCD of %d and %d is: %d\n", num1, num2, result);
28. 
    
29.     return 0;
30. }
31. 
    

Explanation:

1. Input:
   • The user enters two numbers.
2. Logic:
   • The findGCD function uses the Euclidean algorithm:
     • Replace $a$ with $b$ and $b$ with $a \% b$ until $b = 0$.
     • The final value of $a$ is the GCD.
3. Output:
   • The program prints the GCD of the two input numbers.