# C Program to Find GCD or HCF of Two Numbers using For Loop

• Write a C program to find GCD (Greatest Common Divisor) of two numbers using for loop.
• Wap in C to find HCF (Highest Common Factor) of two numbers.

#### Required Knowledge

The highest common factor (HCF) of two or more integers, is the largest positive integer that divides the numbers without a remainder. HCF is also known as greatest common divisor (GCD) or greatest common factor(GCF)

Algorithm to find GCD of two numbers
Let, A and B are two numbers.
• Find minimum of A and B. Let A < B.
• Find the largest number between 1 to A, which divides A and B both completely.

## C program to find gcd of two numbers using for loop

```#include <stdio.h>

int getMinimum(int a, int b){
if(a >= b)
return b;
else
return a;
}

int main() {
int a, b, min, counter, gcd = 1;
/*
* Take two numbers as input from user
*/
printf("Enter two numbers\n");
scanf("%d %d", &a, &b);

min = getMinimum(a, b);

for(counter = 1; counter <= min; counter++) {
/*
* Check, If counter divides both input number
*/
if(a%counter==0 && b%counter==0) {
/* Update GCD to new larger value */
gcd = counter;
}
}

printf("GCD of %d and %d = %d\n", a, b, gcd);

return 0;
}
```

Output
```Enter two numbers
15 50
GCD of 15 and 50 = 5
```
Write a C program to find product of digits of a number using while loop.
Wap in C to multiply the digits of a number.

#### Required Knowledge

To multiply digits of a number we have to remove one digit at a time, we can use '/' division and '%' modulus operator. Number%10 will give the least significant digit of the number, we will use it to get one digit of number at a time. To remove last least significant digit from number we will divide number by 10.

Product of digits of 2534 = 2 x 5 x 3 x 4 = 120

Algorithm to find product of digits of a number
• Get least significant digit of number (number%10) and multiply it to the product variable.
• Remove least significant digit form number (number = number/10).
• Repeat above two steps, till number is not equal to zero.

## C program to find sum of all even numbers between 1 to N using for loop

```#include <stdio.h>
#include <conio.h>

int main() {
int num, temp;
long productOfDigit = 1;

/*
* Take a number as input from user
*/
printf("Enter a Number\n");
scanf("%d", &num);
temp = num;

while(num != 0){
/* get the least significant digit(last digit)
of number and multiply it to productofDigit */
productOfDigit *= num % 10;
/* remove least significant digit(last digit)
form number */
num = num/10;
}

printf("Product of digits of %d = %ld", temp, productOfDigit);

getch();
return 0;
}
```

Output
```Enter a Number
2436
Product of digits of 2436 = 144
```
```Enter a Number
2222
Product of digits of 2436 = 16
```

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