recursion - problem.

**Vber** · 02-23-2003

I have a problem on my book, he wants me to build a program that will print all possible combinations (N-1) that the sum of them will be N.

I have this code as far:

Code:

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

void recur(int n); //our recursive function

int main(void) {
    int nNum;
    
    //get data, check it and act
    printf("Insert a number: ");
    if(!scanf("%d",&nNum)) {
        printf("Invalid input\n"); 
        exit(1);
    }
    
    //call ou recursive function        
    recur(nNum);
    
    //pause and exit
    system("PAUSE");
    return 0;
}

void recur(int n) {
    if(n == 0)
        return;
    else if(n == 1) {
        printf("1");
        return;
    }
    else if(n == 2) {
        printf("11");
        return;
    }
    
    else {
        printf("1");
        recur(n-1);
    }
}

I can't understand what to do next, don't make me the code, just try to explain me how to do it.

Hmm, I cannot use any static variables or loops in the recursive function.

Thanks.

**pinko_liberal** · 02-23-2003

Originally posted by Vber
I have a problem on my book, he wants me to build a program that will print all possible combinations (N-1) that the sum of them will be N.

I couldn't understand what your problem is. Do you want all collections of positive integers that add up to N?

**Gustaff** · 02-23-2003

Hi.

I think this will work:

First read the number in N with scanf(). Then call the following function with these two parameters:

recur ( 1, N-1)

void recur(int N1 , int N2) {

if (N1<=N2) {
printf("%d %d", N1,N2);
recur(N1 + 1, N2 - 1);

Be sure that the number N is non zero, positive, and greater than 1

Ps: close the brackets, i cant find them in this keyboard

**Vber** · 02-23-2003

I forgot to say, I can only pass one parameter.

**pinko_liberal** · 02-24-2003

Are you allowed to pass structures? If so the restriction on the number of variables is rather meaningless.

Code:

#include <stdio.h>

typedef struct info
{
	int i;
	int j;
} info;

void show(info *in)
{
	if(in->i <= in->j)
	{
		printf("%d %d\n",in->i,in->j);
		in->i++;in->j--;
		show(in);
	}
}

#define N 11
int main(void)
{
	info n;
	n.i=0;
	n.j=N;
	show(&n);
	return 0;
}

**quzah** · 02-24-2003

Use a void pointer as your function parameter, and pass it an array of intgers, then type cast it inside the function.

That wouldn't technicly violate your single parameter issue either, and would get around the structure issue if you aren't allowed to use them.

Or hell, just have your parameter be an array of integers.

Quzah.

**pinko_liberal** · 02-24-2003

I think a watertight set of restrictions would be
[list=1][*]dont pass pointers[*]don't pass structures[*]no global or static variables[*] single parameter[/list=1]
or simply give a prototype
like

Code:

int show(int N);

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