PROGRAM 41

Object

Write a program to read a number and print whether it is a prime number or not.

Algorithm

1. Declare integer variables num and i.
2. Declare Boolean variable isPrime=true.
3. Read num.
4. Repeat FOR i = 2 to (num-1) by 1
   • IF num mod i = 0, then
     • Set isPrime = false
     • Break out of loop.
   • [End of IF structure.]
   • [End of FOR loop.]
5. IF isPrime=true, then
   Write “The number is a prime number”.
   ELSE
   Write “The number is not a prime number”.
6. Exit.

Flowchart

C++ Source Code

// program 41
#include<iostream>
using namespace std;

int main()
{
  int num, i;
  bool isPrime = true;

  cout << "Enter a number: ";
  cin >> num;

  for (i = 2; i < num; i++)
  {
    if (num % i == 0)
    {
      isPrime = false;
      break;
    }
  }

  if (isPrime)
    cout << "The number " << num << " is a prime number.";
  else
    cout << "The number " << num << " is not a prime number.";
  return 0;
}

C Source Code

/*program 41*/
#include<stdio.h>

int main()
{
  int num, i;
  printf("Enter a number: ");
  scanf("%d", &num);

  for(i=2; i<num; i++)
     {
     if(num%i==0)
	break;
     }
     if(num==i)
	printf("The number %d is a prime number.", num);
     else
	printf("The number %d is not a prime number.", num);
  return 0;
}

Output

Enter a number: 29
The number 29 is a prime number.