•  Check here for printing an integer in c 
• We have 4 basic data types in c programming language
• int, char, float and double
• For storing numbers or integers we will use int data type.
• Lets see an example program sum of two integers in c programming language.
• To add two integers we need two int type variables and third variable to store result of sum of two integers.
• Its a basic level example program for beginners to understand integer data types

• Please check this below program which prints even numbers from 1 to n.

• Print even numbers in c 
• To print sum of even numbers from 1 to n first we need to get all the even numbers and add them.
• Using for or while loop iterate from 1 to n number and get all even numbers
• sum=sum+evenNumber
• C program to find sum of even numbers using while loop

C program to find sum of even numbers using while loop

• Lets see how to write a c program to print even numbers using c programming.\
• Its a basic example to print only even numbers 
• Use for loop and iterate from 1 to n.
• In each iteration check if number if divisible by 2 (n%2 == 0). if yes then its a even number otherwise it is a odd number.
• C program to print even numbers from 1 to n. 

#2 print even numbers in c using while loop

• Now we will try to print even numbers using while loop
• Only difference is replace for with while loop
• Variable initialization will be done before loop
• condition will be inside while(condition)
• increment or decrement will be last line of while block 
• Lets print even numbers using while loop from 1 to n.

• To find sum of digits of a number in c , we need to get individual numbers and add those numbers.
• First of all read a number from user using scanf.
• Using while loop get individual number 
• Divide the number with 10 so we will get last digit of that number as remainder , once we get that last digit then add it to one variable and divide that number with 10 so it will become one digit less.
• like this we can get all digits and add all those numbers to get sum of digits 
• Sum of individual digits in c program
• c program to find sum of digits of a 3 digit number

correction: here n =number .

# program to find sum of digits of a number in c

1. #include<stdio.h> // include stdio.h
2. //c program to find sum of digits of a number using while loop
3. //write a program to find sum of digits of a number
4. //www.instanceofjava.com
5. int main()
6. {
7.     // declare variables 
8.     int number, remainder, sum = 0;
9.     //read input from user 
10.     printf("Enter a number: ");
11.     scanf("%d", &number);
12. 
    
13.    //iterate until number not equal to zero
14.    // get individual digits and add all those digits to get sum
15.     while(number != 0)
16.     {
17.         remainder = number % 10;
18.         sum += remainder;
19.         number = number / 10;
20.     }
21.   //print sum of digits in c
22.     printf("sum = %d", sum);
23. 
    
24.     getch();
25. }

 Lets discuss a basic c program

• Sum of two integers using c. This might be the first practice program for all users.
• To check sum of two integers , read input from user and store in two corresponding integer variables.
• Also take one more variable to store result of sum of two numbers
• c= a+b
• Print result using printf

The GCD (Greatest Common Divisor) of two numbers is the largest number that divides both of them without leaving a remainder. For example, the GCD of 12 and 18 is 6. In C, there are multiple ways to find GCD using a for loop, while loop, recursion, and the Euclidean algorithm. Let's go through each one.

What Is GCD?

GCD is also known as HCF (Highest Common Factor). It is the greatest number that exactly divides two or more numbers.

• GCD of 12 and 8 is 4
• GCD of 100 and 75 is 25
• If one number is 0, the GCD is the other number

• 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.

#1. GCD of Two Numbers Using for Loop

We loop from 1 to the smaller of the two numbers. Every time both numbers are divisible by i, we update gcd. The last value stored is the greatest common divisor.

#include <stdio.h>

int main() {
    int n1, n2, i, gcd;

    printf("Enter two integers: ");
    scanf("%d %d", &n1, &n2);

    for (i = 1; i <= n1 && i <= n2; ++i) {
        if (n1 % i == 0 && n2 % i == 0)
            gcd = i;
    }

    printf("GCD of %d and %d is %d", n1, n2, gcd);
    return 0;
}

Output:

Enter two integers: 12 18
GCD of 12 and 18 is 6

#2. GCD of Two Numbers Using while Loop (Subtraction Method)

This approach uses the idea that if we keep subtracting the smaller number from the larger one, eventually both values become equal  and that equal value is the GCD.

#include <stdio.h>

int main() {
    int n1, n2;

    printf("Enter two positive integers: ");
    scanf("%d %d", &n1, &n2);

    while (n1 != n2) {
        if (n1 > n2)
            n1 -= n2;
        else
            n2 -= n1;
    }

    printf("GCD = %d", n1);
    return 0;
}

Output:

Enter two positive integers: 48 18
GCD = 6

#3. GCD Using the Euclidean Algorithm (Most Efficient)

The Euclidean algorithm is the most efficient method. It works by repeatedly replacing the larger number with the remainder of dividing the two numbers until the remainder becomes 0. The last non-zero value is the GCD.

#include <stdio.h>

int main() {
    int n1, n2, temp;

    printf("Enter two integers: ");
    scanf("%d %d", &n1, &n2);

    while (n2 != 0) {
        temp = n2;
        n2 = n1 % n2;
        n1 = temp;
    }

    printf("GCD = %d", n1);
    return 0;
}

Output:

Enter two integers: 56 98
GCD = 14

#4. GCD Using Recursion

We can implement the Euclidean algorithm recursively. The base case is when a becomes 0  at that point we return b.

#include <stdio.h>

int gcd(int a, int b) {
    if (a == 0)
        return b;
    return gcd(b % a, a);
}

int main() {
    int n1, n2;

    printf("Enter two integers: ");
    scanf("%d %d", &n1, &n2);

    printf("GCD of %d and %d is %d", n1, n2, gcd(n1, n2));
    return 0;
}

Output:

Enter two integers: 36 60
GCD of 36 and 60 is 12

Comparison of All Methods

Key Points to Remember

• GCD is also called HCF (Highest Common Factor)
• If either number is 0, the GCD is the other number
• The Euclidean algorithm is the fastest and most widely used method
• For negative numbers, convert to positive before computing GCD
• GCD is used in simplifying fractions, cryptography, and LCM calculations

All four approaches give the same result the choice depends on your use case. For interviews and competitive programming, go with the Euclidean algorithm or recursion. For beginners just learning loops, the for loop method is the easiest to follow.