C program for prime number

Answer 1

A number is a Prime number if it is divisible by only 1 and itself. So make use of for loop and check for this condition.

int i,num,flag = 0;//num is the number to check

scanf("%d", &num);

for( i=2; i

if( num%i == 0)//it has other divisors

flag = 1;

}

if( !flag)

printf("The number is prime\n");

else

printf("The number is not prime\n");

Answer 2

#include<stdio.h>

void main()

{

int n = 0, i = 3, count = 0, loop = 0;

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 ( loop = 2 ; loop <= i - 1 ; loop++ )

{

if ( i%loop i )

{

printf("%d\n",i);

count++;

}

i++;

}

}

Answer 3

int isprime(int n) { int t; if ((int) (n/2) * 2 == n) return 0; /* number is even - return false */ for (t=3; t*t<n; t+=2) if ((int) (n/t) * t == n) return 0; /* divisible - return false */ return 1; /* prime - return true */ }

Answer 4

#include<iostream> #include<cmath>

bool is_odd (const unsigned num) {

return num & 1 == 1;

}

bool is_even (const unsigned num) {

return is_odd (num) == false;

}

bool is_prime (const unsigned num) {

if (num<2) return false;

if (is_even (num) == true) return num==2; // 2 is the only even prime

const unsigned max = (unsigned) sqrt (num) + 1;

unsigned div;

for (div=3; div<max; div+=2) {

if (num%div == 0) return false;

}

return true;

}

int main (void) {

std::cout << "Enter a whole number: ";

std::cin >> num;

if (is_even (abs (num)) {

std::cout << "The number is even\n";

}else{

std::cout << "The number is odd\n";

}

if (is_prime (abs (num)) {

std::cout << "The number is prime\n";

}else{

std::cout << "The number is composite\n";

}

}

Answer 5

nee babu