Prime number program

Prime number program in c language

#include 

   main() {

  int n, i = 3, count, c;

  printf("Enter the number of prime numbers required\n");

 scanf("%d",&n);  

if ( n >= 1 ) {

  printf("First %d prime numbers are :\n",n);

 printf("2\n");

 }

 for ( count = 2 ; count <= n ; ) {

 for ( c = 2 ; c <= i - 1 ; c++ ) {

 if ( i%c == 0 )

 break;

 }

 if ( c == i ) { 

 printf("%d\n",i);

 count++; 

 }

 i++;

 }

 return 0; 

}

There are many logic to check prime numbers, one given below is more efficient then above method.
for ( c = 2 ; c <= (int)sqrt(n) ; c++ )
//only checking from 2 to square root of number is sufficient.


C program for prime number or not
#include

 main() { 

 int n, c = 2; 

 printf("Enter a number to check if it is prime\n"); 

 scanf("%d",&n);

 for ( c = 2 ; c <= n - 1 ; c++ ) {

 if ( n%c == 0 ) {

 printf("%d is not prime.\n", n);

 break;

 }

 }

 if ( c == n ) 

 printf("%d is prime.\n", n); 

 return 0; 

}

C program for prime number using function
#include

 int check_prime(int);

 main() {

 int n, result;

 printf("Enter an integer to check whether it is prime or not.\n");

 scanf("%d",&n); 

 result = check_prime(n);

 if ( result == 1 )

 printf("%d is prime.\n", n);

 else

 printf("%d is not prime.\n", n);

 return 0;

 }

 int check_prime(int a) {

 int c;

 for ( c = 2 ; c <= a - 1 ; c++ ) {

 if ( a%c == 0 )

 return 0;

 }

 if ( c == a )

 return 1;

 }