# AMCAT Coding Questions asked in Programming Section Prime Numbers

### Program to print prime numbers between 1 to n

/**
* C program to print all prime numbers between 1 to n
*/
#include <stdio.h>
int main()
{
int i, j, n, isPrime; //isPrime is used as flag variable
/* Reads upper limit to print prime */
printf(“Find prime numbers between 1 to : “);
scanf(“%d”, &n);
printf(“nAll prime numbers between 1 to %d are:n”, n);
/* Finds all Prime numbers between 1 to n */
for(i=2; i<=n; i++)
{
/* Assume that the current number is Prime */
isPrime = 1;
/* Check if the current number i is prime or not */
for(j=2; j<=i/2; j++)
{
/*
* If i is divisible by any number other than 1 and self
* then it is not prime number
*/
if(i%j==0)
{
isPrime = 0;
break;
}
}
/* If the number is prime then print */
if(isPrime==1)
{
printf(“%d is Prime numbern”, i);
}
}
return 0;
}
Note: For checking whether a number is Prime or not we just need to check that the number should not be divisible by any number between 2 to n-1. Apart from that you can also check between 2 to n/2. Since any number more than (n/2)+1 cannot be exactly divided by n except self n.

Output

Find prime numbers between 1 to : 100

All prime numbers between 1 to 100 are:
2 is Prime number
3 is Prime number
5 is Prime number
7 is Prime number
11 is Prime number
13 is Prime number
17 is Prime number
19 is Prime number
23 is Prime number
29 is Prime number
31 is Prime number