**C TUTORIAL**

#

**C PROGRAMS**

Function

➤ Introduction to Function

➤ User-defined Functions

➤ Recursion in C

➤ Storage Classes in C

➤ Scope of Variables

Function Programs in C

➤ Functions Examples in C

➤ Add 2 Numbers Function

➤ Find Sum of N numbers

➤ Largest of Three Numbers

➤ Add Subtract Multiply Divide

➤ Calculator Program Functions

➤ Factorial Program Function

➤ GCD of Two Numbers

➤ Find Power of a Number

➤ Find Reverse a Number

➤ Fibonacci Series Function

➤ Prime Number Function

➤ Palindrome Number in C

➤ Armstrong Number in C

Recursion Programs in C

➤ Recursion Examples in C

➤ Fibonacci Series

➤ Find Factorial

➤ Find GCD or HCF

➤ LCM Using Recursion

➤ Tricky C Programs

Here we will write a C program to find the GCD of two numbers using functions. Previously we have already created a program to find the GCD of two numbers without using functions.

The **GCD (greatest common divisor)**, also called the **greatest common factor**, of two numbers, is the largest number that divides both of them. For example, 4 is the GCD of numbers 12 and 20.

In this program, we will define a function to find the GCD of two numbers. To find the GCD of two numbers, loops are needed to execute the same logic multiple times. Prerequisites for this program:- Introduction to Function in C, User-defined Functions in C, C Program Using Functions Example

## C program to find GCD of two numbers using functions

Program description:- Write a C program to find GCD of two numbers by defining a user-defined function.

```
#include<stdio.h>
int gcd(int a, int b);
int main()
{
int num1, num2;
printf("Enter two numbers : ");
scanf("%d %d",&num1, &num2);
int result = gcd(num1, num2);
printf("The GCD of %d and %d = %d", num1, num2, result);
return 0;
}
// User-defined function to find gcd of two numbers
int gcd(int a, int b)
{
int hcf;
for(int i=1; i<=a && i<=b; i++)
{
if(a%i==0 && b%i==0)
{
hcf = i;
}
}
return hcf;
}
```

Output for the different test-cases:-

Enter two numbers : `12 20`

The GCD of 12 and 20 = 4

Enter two numbers: `20 100`

The GCD of 20 and 100 = 20

The user-defined function gcd calculates the greatest common divisor of the two numbers. The iteration starts with the value

. The gcd must be less than or equal to both numbers, so the condition of for loop is, **i=1**

. If the number (value of variable i) can divide both numbers a and b then, it is the hcf of the numbers. **i<=a && i<=b**

Finally, the result is returned back to the caller function, and the result is displayed to the screen.

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