﻿ C++ Exercises: Check whether a number is prime or not - w3resource

# C++ Exercises: Check whether a number is prime or not

## C++ For Loop: Exercise-5 with Solution

Write a program in C++ to check whether a number is prime or not.

Visual Presentation:

Sample Solution :-

C++ Code :

``````#include <iostream> // Preprocessor directive to include the input/output stream header file

using namespace std; // Using the standard namespace to avoid writing std::

int main() // Start of the main function
{
int num1, ctr = 0; // Declaration of integer variables 'num1' and 'ctr', 'ctr' initialized to 0

cout << "\n\n Check whether a number is prime or not:\n"; // Display a message indicating the purpose
cout << "--------------------------------------------\n"; // Display a separator line
cout << " Input a number to check prime or not: "; // Prompting the user to input a number
cin >> num1; // Reading the input number entered by the user

for (int a = 1; a <= num1; a++) // Start of a 'for' loop from 1 to the input number 'num1'
{
if (num1 % a == 0) // Check if 'num1' is divisible by 'a' without any remainder
{
ctr++; // Increment 'ctr' when 'num1' is divisible by 'a'
}
}

if (ctr == 2) // Check if 'ctr' is equal to 2 (prime numbers have only two factors: 1 and the number itself)
{
cout << " The entered number is a prime number. \n"; // Display a message indicating that the number is prime
}
else {
cout << " The number you entered is not a prime number. \n"; // Display a message indicating that the number is not prime
}
}
``````

Sample Output:

``` Check whether a number is prime or not:
--------------------------------------------
Input a number to check prime or not: 13
The entered number is a prime number.
```

Flowchart:

C++ Code Editor: