C program to find GCD of two Numbers

C program to find GCD of two Numbers


C program to find of two numbers : GCD stands for Greatest common divisor. The greatest common divisor is the largest integer that divides both number1 and number2 without a remainder. GCD is also known as  the greatest common factor (gcf), or highest common factor (hcf).

Lets understand the concept of GCD using an example :

Suppose we want to calculate the GCD of 54 and 24.

Now we need to find the factors(all the that divide 54) of 54. The factors of 54 are :


Similarly, factor of 24 are :


Now the common factors of 54 are 1,2,3,6 out of which 6 is the greatest.

So 6 is the GCD i.e. Greatest common divisor of 54 and 24.

Now let us see how to write a C program to find GCD of two numbers using Recursive Euclid’s algorithm.

C program to find GCD of two numbers :

int gcd(int num1, int num2) {
  if (num2)
    return gcd(num2, num1 % num2);
    return num1 < 0 ? -num1 : num1;
int main()
  int a,b,c;
  printf("\nEnter two numbers : ");
  c= gcd(a,b);
  printf("\nGCD of %d and %d is : %d",a,b,c);
  return 0;

We hope you all have enjoyed the C program to find GCD of two numbers. If you have any issues with the logic or the code ask me in form of comments.


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  5. your gcd program is good. i’m just starting to study c program. can you please help me with this? can you help me build gcd using functions in c program? cheers!

  6. If we know the LCM of two numbers (let’s say A and B) then we can find GCD of A and B using following expression:
    LCM(A, B) X GCDA, B) = A*B