I'm trying to write the function:

int sum(int x, int y)

For this function, I need to return sum of m and n using only increment, decrement and unary -. m and n can be any integers e.g. if m is 4 and n is -5, the return value would be -1

I need to handle the cases where m and/or n is negative. Make use of the properties: m + n = -(-m + -n) and m + n = n + m.

So if the sum is -5 + -4 that can be evaluated as -(5 + 4). Also 5 + -4 can be evaluated at -4 + 5.

When the second parameter is positive use the rule a + b = (a + (b-1)) + 1.

The one and only base case is when the second parameter is zero.

Here is my solution:

```
int sum(int x, int y)
{
if(y == 0)
{
return x;
}
if(x < 0 && y < 0)
{
return -(sum(++x,++y));
}
if(x < 0)
{
return sum(++x,--y);
}
if(y < 0)
{
return sum(--x,++y);
}
if(y > 0)
{
return sum(++x,y-1);
}
return sum(++x,++y);
}
int main()
{
int n1 = -5, n2 = 4;
int add = sum(n1,n2);
cout << add << endl;
int n3 = -3, n4 = -8;
int add2 = sum(n3,n4);
cout << add2 << endl;
int n5 = 13, n6 = -6;
int add3 = sum(n5,n6);
cout << add3 << endl;
int n7 = 5, n8 = -4;
int add4 = sum(n7,n8);
cout << add4 << endl;
int n9 = 16, n10 = 10;
int add5 = sum(n9,n10);
cout << add5 << endl;
return 0;
}
```

After testing this program, the output I am getting is:

-1

1

7

1

26

The second part of the output is not correct. When adding -3 and -8, it is supposed to come out to -11, but it is coming out to 1. Is there anyway I can fix this?