Thread: c programming function. Finding next value

I've written up some code to find out if a value entered is a prime number. I have now extended this piece of code by adding another function to find the next prime number. I'm having a lot of trouble getting it working, mainly (i think) because I either can't get it to stop once it has found the next one, or, it's just printing the value+1 as the next value (even though it might not necessarily be prime).

My code is as follows:

Code:

#include <stdio.h>#include <stdlib.h>
#include <math.h>


int isperfect(int);
int nextperfect(int);


int
main(int argc, char **argv) {
	int value, sum, nextvalue;
	printf("Enter two values: ");
	
	while(scanf("%d", &value) == 1){
		if(value<0){
			printf("Error, negative value!");
			exit(EXIT_FAILURE);
		}
		
		sum = isperfect(value);
		if (sum == value){
			printf("The value %d is perfect.\n", value);
		}
		nextvalue = nextperfect(value);
		printf("The next perfect value is %d.\n\n", nextvalue);
	}
	return 0;
}


int
isperfect(int value){
	int divisor, sum = 0;
	
	for(divisor=1; divisor<value; divisor++){
		if(value%divisor == 0){
			sum = sum+divisor;
			printf("The divisor value is = %d, and the value is %d\n", divisor, value);
		}
	}
		
	return sum;
}


int
nextperfect(int value){
	int nextvalue, sum, nextfound;
	
	for(nextvalue = value+1; nextfound == 0 ; nextvalue++){
		sum = isperfect(nextvalue);
		if (sum == nextvalue){
			nextfound = 1;
		}
	}
	
	return nextvalue;
}

Originally Posted by Tigertan

I've written up some code to find out if a value entered is a prime number.

No, you've written code to find out if a value is a perfect number.

Bye, Andreas

Originally Posted by AndiPersti

No, you've written code to find out if a value is a perfect number.

Bye, Andreas

Ahh sorry, yes I meant perfect number! I've been writing up all sorts of programs over the past few days!

Originally Posted by Salem

> int nextvalue, sum, nextfound;
...
> for(nextvalue = value+1; nextfound == 0 ; nextvalue++)

What is the initial value of nextfound?

Why do i need to initialize nextfound?? That's just my guard.. isn't it okay like that?

Local variables that have not been assigned a value, just have a random value. It's unlikely that nextfound would happen to be equal to 0.

Global int variables ARE assigned the value of zero, when they're created.