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. Let us start by understanding what is a prime number.
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.
To understand the following program, you should have a basic idea about the following topics in C++ programming.
Check Prime Number in C++
The program takes a user input for a number that needed to be checked for prime number. Since 0 and 1 are not prime numbers so we first check them using the if statement. And if the number is other than 0 and 1 the execution control goes to the else part of the statement.
C++ Program to Check Whether a Number is Prime or Not
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 | #include <iostream> using namespace std; int main() { int i, num, flag; cout << "Enter a positive integer: "; cin >> num; // checking for 0 and 1 if (num == 0 || num == 1) { flag = 1; } else { for (i = 2; i <= num / 2; ++i) { if (num % i == 0) { flag = 1; break; } } } if (flag == 0) cout << num << " is a prime number"; else cout << num << " is NOT a prime number"; return 0; } |
Output:
Enter a positive integer: 13
13 is a prime number
You may go through the following program of prime numbers in C++.