## Feb 15, 2020

### 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 (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: