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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Big list of c program examples

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

1. Check out programming video tutorials on this YOUTUBE Channel

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

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

4. tanku

5. 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

6. thanx alot..:)

7. Learn basic of c programming from Programmingcampus

8. what is the use of static int?

9. 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);
}
}
}

10. #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();
}