MFC Visual C ++代码以检查有效的数字条目

Question

I have this MFC app with the following piece of code to check for the validity of numbers entered using a edit control in the app. Its validated as a string of chars.

bool invalid = FALSE;
int string_length = InputEdit.GetWindowText(text, 10);
if (text[0] == '-1')
    for(i=1; i<string_length; i++)
        if((text[i] < '0' || text[i] > '9' ) && text[i] != '.'){
            MessageBeep(MB_ICONEXCLAMATION);
            Reactive_Const_Status_Text.SetWindowText("Invalid AA Value");
            invalid = TRUE;
        }
else
    for(i=0; i<string_length; i++)
        if((text[i] < '0' || text[i] > '9' ) && text[i] != '.'){
            MessageBeep(MB_ICONEXCLAMATION);
            Reactive_Const_Status_Text.SetWindowText("Invalid AA Value");
            invalid = TRUE;
        }

if(!invalid){   
    double temp_value = atof(text);
    reac.VelAA  = temp_value;
}

So this edit control allows users to enter negative numbers. However can someone please shed some light about what this line "if (text[0] == '-1')" does in the code ? Is it checking for negative numbers and if so why does it use '-1' ? Secondly, I'm wanting to convert this code to C# and so how can I convert this line ?

Thanks in advance

Answer 1

Actually, this code is also checking for negative numbers. The first for loop checks from second digit onwards.

The line if (text[0] == '-1') is supposed to be if (text[0] == '-')

I guessed it this way because in C++ single quotes can be used only for single character and not for a string with more than one character.

In C# the same line if (text[0] == '-') will work.

Thanks.