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In this tutorial, we will learn how to swap two numbers in C program. Before that, if you may go through the following topics in C that are used in this program.

• C operators
• C data-types

C Program to Swap Two Numbers using temporary variable

The program takes two number inputs from the user that needed to be swapped. And using a third variable, we swap the value. The third variable used is named temp in the program.

#include<stdio.h>

int main()
{
    int a, b, temp;
    
    printf("Enter a: ");
    scanf("%d", &a);
    
    printf("Enter b: ");
    scanf("%d", &b);
    
    temp = a;
    a = b;
    b = temp;
    
    printf("The swapped values a: %d and b: %d", a, b);
    
    return 0;
}

Output:

Enter a: 10
Enter b: 20
The swapped values a: 20 and b: 10

You may want to check the following swapping program in C.

• Swap Numbers Without Using Temporary Variables in C

In this tutorial, we will write a C program to swap two numbers without using a temporary variable. There are two ways to swap variables.

1. Using + and –
2. Using * and /

Let us go through each of them with a C program. You may check out the following program.

• C Program to Swap Two Numbers using third variable

C Program to Swap Two Numbers without using Third Variable

1. Using + and –

#include<stdio.h>

int main()
{
    int a, b;
    printf("Enter a: ");
    scanf("%d", &a);
    
    printf("Enter b: ");
    scanf("%d", &b);
    
    
    a = a + b;  //a = 10 + 20 = 30
    b = a - b;  //b = 30 - 20 = 10
    a = a - b;  //a = 30 - 10 = 20
    
    printf("The swapped values a: %d and b: %d", a, b);
    
    return 0;
}

Output:

Enter a: 10
Enter b: 20
The swapped values a: 20 and b: 10

2. Using * and /

#include<stdio.h>

int main()
{
    int a, b;
    printf("Enter a: ");
    scanf("%d", &a);
    
    printf("Enter b: ");
    scanf("%d", &b);
    
    a = a * b; //a = 10 * 20 = 200
    b = a / b; //b = 200 / 20 = 10
    a = a / b; //a = 200 / 10 = 20
    
    printf("The swapped values a: %d and b: %d", a, b);
    
    return 0;
}

Output:

Enter a: 10
Enter b: 20
The swapped values a: 20 and b: 10

Note that the swapping using / and * will not work if one of the swapping values is zero (0).

In this C programming example, we will learn about the Prime Number program in C. We specifically write a program to check the entered number is prime or not.

Prime Number:

A Prime Number is a number that is only divisible by 1 and itself. Example: 2, 3, 5, 7, 11, 13, 17, etc. These numbers are only divisible by 1 and the number itself.

Note:
0 and 1 is not a prime number and 2 is the only even and smallest prime number.

• C Program to Print Prime Numbers up to a Given Number
• C program to Print Prime Numbers in a Given Range (max & min)

You must know the following topics in C first:

• for loop in C
• if statement in C
• data-types in C

C Program to Check Whether a Given Number is Prime or Not

#include <stdio.h>

int main()
{
  int num, i, flag = 0;

  //user input
  printf("Enter the number: ");
  scanf("%d", &num);

  for (i = 2; i <= num / 2; ++i)
  {
    // checking for non-prime
    if (num % i == 0)
    {
      flag = 1;
      break;
    }
  }

  //checkinh for the entered number is 1 or not
  //because 1 cannot be a prime number
  if (num == 1)
  {
    printf("1 is not a prime number.");
  }
  else
  {
    if (flag == 0)
      printf("%d is a prime number.", num);
    else
      printf("%d is not a prime number.", num);
  }

  return 0;
}

Output:

//Run 1
Enter the number: 13
13 is a prime number.

//Run2
Enter the number: 1
1 is not a prime number.

You may go through the following C program on the prime number.

• C Program to Print Prime Numbers up to a Given Number
• C program to Print Prime Numbers in a Given Range (max & min)