C Program to Print Alternate Prime Numbers from 1 to n

Ex: Write a C program to print alternate prime numbers from 1 to n. How to write a C program to print alternate prime numbers from 1 to n. C program to print alternate prime numbers from 1 to n.

Input from user:

Enter the number: 100

Expected output:

2 5 11 17 23 31 41 47 59 67 73 83 97

• What is prime number?

Prime number means a number that is divisible only by 1 and itself.

  Step by step logic of the given program:

1. Accept input from user declare variable say no.

2. Declare e=2.

3. Run one outer for loop from 1 to no:

for(i=1;i<=no;i++)

4. Run one inner for loop from 1 to i and inside that check condition if i%j == 0 then increment c by 1:

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

  {

  if(i%j==0)

   {

  c++;

   }

  } 

5. After that outside the inner for loop check if c==2 (it means if given number is prime) then, inside that if-statement check one more condition if e%2==0 means if e is even number then print value of i (it prints   prime numbers only if e is completely divisible by 2, in short it prints alternate prime numbers):

if(c==2)

 {

 if(e%2==0)

 { 

 printf("%d ",i);

 }

6. After that, Outside the block of inner if statement increment value of e by 1.

7. Last make c=0.

  Program to Print Alternate Prime Numbers:

#include<stdio.h>

void main()

{

 int no,i,j,c=0,e;

 printf("Enter the number:\n");

 scanf("%d",&no);

 e=2;

 printf("Alternate Prime Number's Are:\n");

 for(i=1;i<=no;i++)

  {

  for(j=1;j<=i;j++)

  {

  if(i%j==0)

   {

  c++;

   }

  } 

 if(c==2)

 {

 if(e%2==0)

 { 

 printf("%d ",i);

 }

    e=e+1;

 }

 c=0;

 }

}

Above Program show's the following output: