C Program to calculate difference of n natural numbers using recursion and recursion is must to use

I wrote the code but I am getting the wrong output. Say for example when I enter 5 the output I am getting is 3 instead it should be -5. Please point out my mistakes and provide me some solutions.

#include <stdio.h>
int difference(int a);

int difference(int a)

{
    if (a != 0)
    {

        return (a - difference(a - 1));
    }
    else
    {
        return 0;
    }
}
int main()

{
    int n;

    printf("Enter number until which you want difference of:\n");

    scanf("%d", &n);

    printf("The difference of numbers is %d", difference(n));

    return 0;
}

>Solution :

As this seems home work, just the error cause:

d 5 = [a] 5 - d 4 = [k] 5 - 2 = 3
d 4 = [b] 4 - d 3 = [j] 4 - 2 
d 3 = [c] 3 - d 2 = [i] 3 - 1
d 2 = [d] 2 - d 1 = [h] 2 - 1
d 1 = [e] 1 - d 0 = [g] 1 - 0
d 0 = [f] 0

Bad algorithm, bad, bad.

If difference between two numbers is meant:

int difference(int a, int b)
{
    if (a == b)
    {
        return 0;
    }
    else if (a > b)
    {
        return 1 + difference(a - 1, b);
    }
    else //if (a < b)
    {
        return difference(b, a);
    }
}

Even if this is home work, a solution:

int identityByRecursiveDifference(int a)
{
    return a == 0 ? 0 : 1 + identityByRecursiveDifference(a - 1);
}

Here the difference is 1.

int identityByRecursiveDifference(int a)
{
    if a == 0 {
        return 0;
    }
    int half = identityByRecursiveDifference(a / 2);
    return 2 * half + (a % 2);
}

Here the difference is half; exact with even a or about with odd a.
a % 2 is remainder by division of 2.

Less recursion, not a steps but ²log a steps.