C++ Program to Check Prime Number

Last Updated:

What is Prime Number?

A positive integer that is divisible only by itself and 1.

Tips: It is recommended to use our online Prime Numbers calculator for better understanding.

Examples

The following table provides few examples of prime numbers.

NumberDivisorResult
13 1, 13 Prime Number
15 1, 3, 5, 15 Not a Prime Number
47 1, 47 Prime Number

Using for loop

In the following example, we will check whether the given number (7) is a Prime number or not using for loop.

Example

C++ Compiler
#include <iostream> using namespace std; int main() { int num = 7; int i = 1; int count = 0; for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) cout << num <<" is a prime number"; else cout << num <<" is not a prime number"; return 0; }

Using while loop

In the following example, we will check whether the given number (7) is a Prime number or not using while loop.

Example

C++ Compiler
#include <iostream> using namespace std; int main() { int num = 7; int i = 1; int count = 0; while(num >= i) { if(num % i == 0) count++; i++; } if(count == 2) cout << num <<" is a prime number"; else cout << num <<" is not a prime number"; return 0; }

Using do while loop

In the following example, we will check whether the given number (7) is a Prime number or not using do while loop.

Example

C++ Compiler
#include <iostream> using namespace std; int main() { int num = 7; int i = 1; int count = 0; do{ if(num % i == 0) count++; i++; }while(i<=num); if(count == 2) cout << num <<" is a prime number"; else cout << num <<" is not a prime number"; return 0; }

Prime Numbers between the Given Range

In the following example, we will find all the Prime numbers between 1 and 20.

Example

C++ Compiler
#include <iostream> using namespace std; int main() { int start = 1; int end = 20; int count = 0; int i = 1; cout << "Prime Numbers between " << start <<" and " << end <<": \n"; for(start=start; start<=end; start++) { for(i=1; i<=start; i++) { if(start % i == 0) count++; } if(count == 2) cout << start << " "; count = 0; } return 0; }

Check Whether the Given Number is Prime or Composite

In the following example, we will check whether the given number is a Prime number or Composite number.

Example

C++ Compiler
#include <iostream> using namespace std; int main() { int num; int i = 1; int count = 0; cout << "Enter a (int) number: "; cin >> num; for(i=1; i<=num; i++) { if(num % i == 0) count++; } if(count == 2) cout << num <<" is a prime number"; else cout << num <<" is a composite number"; return 0; }