Negative Numbers

i have a as an integer but the output would be -a. does anyone not understand? here..if a user enters 5 the output would be -5. if a user enters -5 the output would be 5. How do i do this using this code:
[code]
#include <iostream.h>

void main()
{
cout << "Enter a: ";
int a;
cin >> a;
if(a == //i have no idea what to put here)
{
//something
}
}

Code:

---

#include <iostream.h>

void main()
{
 int a;
 cout << "Enter a: ";
  a=0;
  cin >> a;
  if(a) {
    a = a* (-1);
    cout << a;
  }
  return;
}

---

Code:

---

#include <iostream.h>

void main()
{
 int a;
 cout << "Enter a: ";
  a=0;
  cin >> a;
  if(a) {
    a = a* (-1);
    cout << a;
  }
  return;
}

---

hmm why are you multiplying it with -1, is there a special reason for it?
because this also seems to work, or am I overlooking something?

PHP Code:

---

#include <iostream>

using namespace std;

int main(){
    int i;
    cout << "Enter i" << endl;
cin >> i;
    cout << -i << endl;
} 


---

Yes. if(a) {} should really puke when value is zero.
The 'specs' are a bit scanty to say the least :D

unary - operator does exactly that. And for the if(a):
if(cin.good()) {}
checks if cin was able to read a number.