How to make error messages?

[platypus1130]

Lets say I made a square root function and I want an error message if the input is negative. How...

EDIT: This is just an example. I want to make errors for other things as well. I'm asking if there is a specific way to test for errors and then output an error message instead of returning a value.

[eker676]

if(value < 0)
{
  cout << "Error: Negative Number entered\n";
}

[seymore15074]

Throw an exception?

[jsmith]

Why not make the function take an unsigned and avoid the problem in the first place?

[seymore15074]

jsmith, would that still apply if the input was determined at run-time? I am under the impression that using unsigneds would only give compiler errors if a literal (or a value available at compile-time) was used.

[jsmith]

If the function is declared as

unsigned sqrt( unsigned );

then passing any constant or variable into the function will generate a compile error if the actual parameter is signed.

[seymore15074]

Oh yes; it wouldn't implicitly cast to an unsigned... Thanks.