C++ Program to Check Prime Number

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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
131, 13Prime Number
151, 3, 5, 15Not a Prime Number
471, 47Prime 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; }

Output

7 is a prime number

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; }

Output

7 is a prime number

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; }

Output

7 is a prime number

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; }

Output

Prime Numbers between 1 and 20: 2 3 5 7 11 13 17 19

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; }

Output

Enter a (int) number: 13 13 is a prime number

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