Prime Number Program-Best Guide for Prime Number Program with output - Programmer's Mind

What is a prime number??

A Prime number is a natural number, which is evenly divisible only by 1 and itself.
Click here more about Prime Number
Armstrong Number
Strong Number
Perfect Number

The logic used to check whether the given number is prime or not is as follows

Take the Number from the user
Count the factors of the Number
If the count is 2,then it is a Prime Number
Otherwise it is not a Prime Number

Program to check whether the given number is prime or not:

#include<stdio.h>

void main()

{

int num,i,count=0;

printf("Enter Number\n");

scanf("%d",&num);

for(i=1;i<=num;i++)

{

if(num%i==0)

{

count++;

}

if(count==2)

{

printf("%d is a Prime Number",num);

}

else

{

printf("%d is not a Prime Number",num);

}

Output:

Another fact about prime numbers is that except 2 and 3,every prime number leaves remainder 1 or 5 when it is divided by 6.But Every number which leaves remainder 1 or 5 when divided by 6 is not a Prime.Let us construct a program to check whether prime numbers leaves remainders (1 or 5) or not.For proof click here

Logic for this program

Take the number
Divide the number by 6
Print the Remainder

Program:

#include<stdio.h>

void main()

{

int num,rem;

printf("Enter Number\n");

scanf("%d",&num);

rem=num%6;

printf("Remainder is %d",rem);

}

Output:

Check for different prime numbers and observe the remainders.As i mentioned earlier,some other numbers also leaves remainders 1 or 5.In above output,55 and 65 are not primes but leaves remainders 1 and 5 respectively.

Armstrong Number

Strong Number

Perfect Number