## INDEX

### Prime number program in c using recursion

C code to check a number is prime number or not by recursion:

#include<stdio.h>

int isPrime(int,int);

int main(){

int num,prime;

printf("Enter a positive number: ");
scanf("%d",&num);

prime = isPrime(num,num/2);

if(prime==1)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);

return 0;
}

int isPrime(int num,int i){

if(i==1){
return 1;
}else{
if(num%i==0)
return 0;
else
isPrime(num,i-1);
}
}

Sample output:

Enter a positive number: 13
13 is a prime number

C code to check a number is prime number or not without recursion:

#include<stdio.h>

int isPrime(int);

int main(){

int num,prime;

printf("Enter a positive number: ");
scanf("%d",&num);

prime = isPrime(num);

if(prime==1)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);

return 0;
}

int isPrime(int num){

int i=2;

while(i<=num/2){
if(num%i==0)
return 0;
else
i++;
}

return 1;
}

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Anonymous said...

for better program u can divide till square root of number.
while(i<=Math.sqrt(num))

Mun said...

wap to c using for loop check number is prime or not.

Anonymous said...

Dude good collection, but improve complexity of the program as well.

Anonymous said...

tanku

Krrish Jaya said...

Hi,
The following code is working correctly with recursive function for find out prime or not.
char isPrime(int);

int main(){

int num;
char prime;

printf("Enter a positive number: ");
scanf("%d",&num);

prime = isPrime(num);
printf("\nPrime=%d\n",prime);

if(prime==1)
printf("%d is a prime number",num);
else
printf("%d is not a prime number",num);

return 0;
}

char isPrime(int num){

static int i=2;
if(i<=num/2)
{
if(num%i==0)
{
printf("In \"not prime loop\" i=%d,num=%d\n",i,num);
return 0;
}
else
{
i++;
printf("In \"prime loop\" i=%d,num=%d\n",i,num);
if(!(isPrime(num))){
printf("ISprime fun exit at i=%d,num=%d\n",i,num);
return 0;}

}
}

return 1;

Thnks,

Krish

Anonymous said...

thanx alot..:)

Anonymous said...

Learn basic of c programming from Programmingcampus

Anonymous said...

what is the use of static int?

Anonymous said...
Anonymous said...

The following is the correct C code to check a number is prime number or not by recursion
#include
#include
int primeno(int, int);
int main()
{
int num, check;
printf("Enter a number: ");
scanf("%d", &num);
check = primeno(num, num / 2);
if (check == 1)
{
printf("%d is a prime number\n", num);
}
else
{
printf("%d is not a prime number\n", num);
}
getch();
return 0;
}
int primeno(int num, int i)
{
if (i == 1)
{
return 1;
}
else
{
if (num % i == 0)
{
return 0;
}
else
{
return primeno(num, i - 1);
}
}
}

கார்த்திக் said...

#include
#include
int i=2,x=1;
void dd(int u)
{
if(i<u)
{
if(u%i==0)
x=x*0;
else
x=x*1;
i++;
dd(u);
}
}
void main()
{
int n;
clrscr();
printf("enter ");
scanf("%d",&n);
dd(n);
if(x==0)
printf("not");
else
printf("pr");
getch();
}

Unknown said...

I need program to find first n prime numbers. Like first 3 prime numbers (1,2,3) using recursion

venkata subbaiah said...

Code for prime number checking by using recursion..

Int prime (int n,int i)
{
If(i<n)
{
If(n%i==0)
Return 0;
Else
Return prime (n,i+1)
}
}
Void main ()
{
Int n,i=2,check;
Clear();
Printf("/n enter any one number");
Scanf("%d",&n);
Check=prime (n,i);
If(check==0)
Printf ("/n not a prime number");
Else
Printf ("/n a prime number");
Getch ();
}

Thanks

mani said...

what is the meaning of return 0..
at this place how it runs and how it exicutes..