Thread: Recuration Prime Numbers

Hi all,

I wrote a code that finding the N'th prime number according to an index that given, for example: "Prime number #7 is 17."

my program working for very small index's, and I need it to work on an index till 1000, but after app. 50 I get "Stuck overFlow"
I need some help to improve my code.
(the int findNthPrime(int n); prototype is a must).

Thanx in advance.

my code:

Code:

#include <stdio.h>
#include <string.h>
#define INPUT_LEN 256

int print_menu(int menu);
int findNthPrime(int n);
int checkingINPUT_LEN(char choise[],int x);
int findingprime(int number,int i,int counter,int j);

void main()
{
	 print_menu(1);
}
int print_menu(int menu)
{
	int  n=0,temp;
	char choice[INPUT_LEN]={0};

	printf("Welcome to Math-N-Stuff.\nPlease select an option from the following menu (1, 2, 3 or 4)."
		   "\n0. Quit.\n1. Finding prime number:\n2. Find all primes on a list of numbers.\n"
		   "3. Calculate mathematical formula.\nPlease enter your choice\n");
	gets(choice);	
	
	switch(choice[0]){
		case '0':
			/*Exit the program*/
			printf("Quitting.\nGoodbye");
			return -1;

		case '1':
			/* Option one, Finding  the Nth prime number,
			   and the smallest prime number bigger then N */

			printf("Please enter parameter:\n");
			scanf("%d",&n);
			//getchar();
			if(n>1000){
				printf("\nParameter too big,\n\n");
				break;
			}
			if(n<1){
				printf("\nIlegal input in option 1\n\n");
				break;
			}
			temp=findNthPrime(n);
			print_menu(1);
			return -1;

		case '2':
			/*Finding all Prime's in arr*/
			print_menu(1);
			return -1;

		case '3':
			/*The function Calculates a formula given in char*/
			print_menu(1);
			return -1;
		
		default:
			/*if the input is wrong*/
			printf("Ilegal input in main menu.\n\n");
			print_menu(1);
			return -1;

	}
	return -1;		
}

int findingprime(int number,int i,int counter,int j)
{
	if(counter==number)
		return --i;
	if(i%j==0){
		i++;
		j=1;}
	if(j>=i/2){
		i++;
		counter++;
		j=1;}
		findingprime(number,i,counter,j+1);
}
int findNthPrime(int n)
{
	int i=2,j=2,counter=1,prime=0;
	prime=findingprime(n,i,counter,j);
	printf("Prime number #%d is %d.\n\n",n,prime);
	return prime;
}