FIND PRIME NUMBER IN C++

What is a PRIME NUMBER?

" A Natural number greater than 1 which has only two divisor 1 and itself is called prime number ".

For Example:  

5 is prime, because it has only two divisors 1 and itself.

C++ Program To Find Prime Numbers

1. #include<iostream.h>
2. #include<conio.h>
3.         void main()
4.         {
5.          //clrscr();
6.          int number,count=0;
7. cout<<"ENTER NUMBER TO CHECK IT IS PRIME OR NOT ";
8.           cin>>number;
9.            for(int a=1;a<=number;a++)
10.                {
11.                 if(number%a==0)
12.                    {
13.                   count++;
14.                    }
15.                }
16.        if(count==2)
17.          {
18.           cout<<" PRIME NUMBER \n";
19.          }
20.        else
21.          {
22.           cout<<" NOT A PRIME NUMBER \n";
23.          }
24.        //getch();
25.        }

UNDERSTANDING PRIME NUMBERS PROGRAM LOGIC

•      To make logic first think about PRIME NUMBER definition that a number which divides by 1 and itself.
•    So we have make a condition like that in which user will enter a number and our program will check it by dividing it from 1 up to itself.
•    To check that how much times it has divided to numbers from 1 to itself we take a variable and increment it each times when a number is divided.
•    In C++ CODING we take a FOR LOOP which will start from 1 up to number that has entered to check whether it is PRIME NUMBER or not with in FOR LOOP we set an IF condition and placed counter (count++) variable in its body so whenever a number from 1 to number which has entered to check divides than IF condition becomes true and counter variable will be incremented.
•    When FOR LOOP is completed we check from IF condition that if counter variables value is equal to 2 than number is PRIME else NUMBER IS NOT PRIME.
•    Because if number divided two times by 1 and itself counter variable will incremented two times if more than two times counter variable will have value greater than 2. 

Prime number program image view

C++ program to find prime numbers 

Sample Output:

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Recommended: For fast learning change the logic and do experiment with codes.

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