Prime numbers are the numbers which have only two factors, 1 and the number itself. That means, they are not divisible by any number other than one and the number itself.

In this article, we’ll learn how to check whether a number is prime or not, with and without using function. But before that, we’ll write a program to print prime numbers from 1 to 200.

This C program prints prime numbers from 1 to 200. This algorithm can also be used to check whether a number is prime or not.

**Program:** C program to print prime numbers from 1 to 200

#include<stdio.h>intmain() {intn,i,flag; for(n=1; n<=200; n++) /*iterate over numbers from 1 to 200*/ { flag=0; for(i=2;i<=(n/2);i++) { if((n%i)==0) /* check prime or not*/ { flag=1; break; } } if(flag==0) printf("%d ",n); } printf("\n"); return 0; }

**Output**: Prime numbers from 1 to 200

`1 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199`

Now, we’ll write a program to check whether a number is prime or not using function. The same algorithm is used to serve this purpose.

## Program: C program to check whether a number is prime or not using function

#include<stdio.h>intcheckPrime(int);intmain() {intn,i,flag; printf("Enter a number: "); scanf("%d", &n); flag = checkPrime(n); if(flag == 1) printf("%d is not a prime number.", n); else printf("%d is a prime number.", n); printf("\n"); return 0; }intcheckPrime(inta){inti; for(i=2;i<=(a/2);i++) { if((a%i)==0) /* check prime or not*/ return 1; } return 0; }

**Output:**

**Sample output #1:**
Enter a number: 4337
4337 is a prime number.
**Sample output #2:**
Enter a number: 4239
4239 is not a prime number.

**Challenge:** Write C program to check whether a number is prime or not in the comments.

In this article, we learnt to write program in C to check prime numbers and to print prime numbers between two numbers.

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