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C++ Program to Check if a Number is Prime Number or not

January 7, 2021

C++ Program to Check Whether the Number is Prime or Not

Prime number is a number which can be divided by 1 and itself i.e. a number which can not be divided by any other number other than 1 or itself is a prime number.
 
Example: 2,3,5,7,11….so on  are the prime number as we can see they only have two divisors, 1  and the number itself.
Program to check whether a number is a Prime Number or Not

Algorithm:-

  1. Take input number n
  2.  Initialize i=1
  3.  Initialize div=0
  4.  we have to count all the divisor of number from 1 to n
  5.  run a loop from i=1 to n
    1. if n%i==0  (if n is divisible by i)
      1. increment div, div++
    2. increment i by 1 ,i++
  6. check div, if div==2 display prime, else display not prime

C++ Code:-


//C++ Program
//Check Prime or Not
#include<iostream>
using namespace std;
int main()
{
    int i,num,div=0;        //initializing variables
    cout<<“Enter number:”;  
    cin>>num;           //user input
    for(i=1;i<=num;i++)     //checking for number of divisor
    {
        if(num%i==0)
        {
            div++;              
        }
    }
    if(div==2)          //no divisors other than 1 and itself
    {
        cout<<num<<” is a prime number”;
    }
    else
    {
        cout<<num<<” is not a prime number”;
    }
    return 0;
}

    Output

    Enter number:31
    31 is a prime number
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