C program to find prime number?

Answer 1

I am providing a succinct and easy to understand version of the program. I have run it in 3-4 compilers and it works perfect. Mind you, you should not enter a number more than 2147483647 (which is the largest number a variable can process in C!). If you do, no problem, but it will display all numbers above it, including the even numbers to be prime. So here you are:

#include

#include

main()

{

long int a,b,c;

printf("Enter the number: ");

scanf("%ld",&a);

for (b=2;b

{

c= a%b;

if (c==0)

goto cool;

}

printf("\nThe number is goddamned prime!");

goto fool;

cool: printf("\nThis ain't a Prime number you dumbo!");

fool: printf("\n");

}

By the way I am not sure what your query really was. I gave the above program to check whether a number is prime or not. If you mean to generate prime numbers between 2 (which is of course the first prime number) and a given number g and also want to know the number of prime numbers between the two, well here is it:

#include

#include

main()

{

long int a=2,i=2,c,count=0,g;

printf("Prime numbers upto what number should be generated? ");

scanf("%ld",&g);

printf("\nFollowing is the list of prime numbers:\n");

while (a<=g)

{

for (i=2;i

{

c=(a%i);

if (c==0)

goto cool;

else

continue;

}

printf("\n%ld",a);

++count;

cool: ++a;

}

printf("\nTotal number of prime numbers between 2 and %ld is %ld. ",g,count);

}

For both these programs, simply copy-paste them into your compiler and have your result. Hope you got what you wanted...

Answer 2

#include<stdio.h>

#include<conio.h>

main()

{

int i,j,n;

printf(" Enter the number upto which you want to find prime number ");

scanf("%d",&n);

printf("\n");

for(i=2;i<=n;i++)

{

for(j=2;j<=i-1;j++)

if(i%j==0)

break;

if(i==j) printf("\n\t%d",i);

}

getch();

}

//for example if u want to find prime number between 1 to 100 enter 100..

// u will get prime number between 1 to 100

//tested in bloodshed dev c++

Answer 3

#include<stdio.h>

#include<conio.h>

void main()

{

int n;

clrscr();

printf("\nenter a number...\n");

scanf("%d",&n);

if (n!=2 && n%2==0)

printf("%d isn't prime..", n);

else

printf("%d is either prime or not..", n);

getch();

}