Developer & Internet Marketer

Welcome to my blog.

Sed sed leo sit amet elit sagittis fermentum. Nulla posuere commodo erat. Nam ac nunc ipsum, id espara tincidunt orci. Quisque adipiscing molestie dolor, ut congue sem porta et. Sed sapien urna, auctor et accumsan ut, accumsan sit amet dui. Nunc tristique interdum magna, dictum volutpat sem. Nam ac nunc ipsum, id espara tincidunt orci. Sed sapien urna, auctor et accumsan ut.

C++ Program For Prime Number – Check if a Number is Prime or Not!

May 1, 2017wp-himu5 Comments

In this tutorial, we’re going create a C++ program for Prime Number that will be able check if the given number is Prime or not. To understand the program or code you have to understand what are prime/composite numbers are and how to identify them.

Complete definition, a prime number (or a prime) is a natural number greater than 1 that has no positive divisors other than 1 and itself. A number that is not a prime is called composite, except 1 because 1 is considered neither a composite nor prime.

5 is a prime because only 1 and 5 can divide it, whereas 6 is a composite because it has the divisors 2 and 3 in addition to 1 and 6.

A prime number is a number that has NO positive divisors other than 1 and itself.

Example of Numbers that are Prime (between 1-100) : 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97 and more (see the image below).

 C++ Program For Prime Number

Prime Numbers 1-1000

How C++ program will Check Prime numbers?

Suppose, the number we want to test is N then this program will divide the number N with all the numbers between 1 to N because if the number N is divisible by a number other then 1 or N then it’s not a prime.

Note: Actually we don’t really need to divide N up to N-1 to check if it is a prime or not because logically if there exist any number that can divide N then it can be find before N/2 division.

Suppose N is 35 then the program will divide 35 with 2, 3, 4, 5… up to 16 and check whether it is divisible by any of the number other than 1 and 37 or not. Here 35 is divisible by 5 and 7 therefore the program can easily tell that 35 is not a prime number.

C++ Program For Prime Number

Now we had learned about prime numbers and we will apply this knowledge into our C++ program for prime number.

[codesyntax lang=”cpp” tab_width=”5″ title=”c++ program to check for prime numbers”]

// C++ program to check whether the given number is Prime or Not!


void main()

int num, count=0;

cout<<"Enter a number :";

for(int i=2; i<num; i++)

   cout<<"Prime number";
   cout<<"Not a Prime number"; 




If you know what prime numbers are and knows a little programming then there is no need to explain this program but I am still going to explain a little about the program.

STEP1: The program is asking for a number, num.

STEP2: A loop starts from 2 to num-1 and divides num with these numbers,
If division is successful (when remainder is 0) then count is increased by 1 and loop ends (using break keywords).

STEP3: When the loop ends the value of count is checked for 0 (zero). 0 means no successful division and proves the number is a prime number.

I hope the above C++ Program for Prime Number was easy. Are you facing any problem?


This article has 5 comments
  1. Aizat Azami
    November 3, 2013

    Excuse me, I try your programme. All the prime number is correct. Only num 4. It is include in the prime number.

      November 11, 2013

      hmm…?? I don’t think so…

      • Naks Saxena
        January 8, 2014

        Aizat Azami is correct.
        Num 4 is included in prime.
        use num instead of num/2 to solve this.

          January 11, 2014

          Yup you are right dude and Aizat too. I noticed it a few days after I commented before. Thanks for the interaction everyone.

          • kashif Gillani
            February 19, 2014

            Number 4 is not a prime.. I tried it.. Program code is correct.. Thanks sir

Leave a Reply
www.edatastyle.com www.introducingsomething.com