isdigit ()

**mackol** · 01-18-2003

heya guys
i am having a little problem with isdigit in C++ even though i have used it in the past in C

the situation is very simple.
someone types in values in an integer array.
i use a loop and go through each element and check if its a digit. even though they are all integers it sitll returns false

heres the code

Code:

int checkAlpha (const student x)
{
	for (int i = 0; i < NumLabGrades; i++)
	{
		if (x.lab_grade[i] < 0 || x.lab_grade[i] > 25) return 0;
		if (!(isdigit (x.lab_grade[i]))) return 0;
	}
	return 1;
}

thanks

**Sebastiani** · 01-18-2003

>> if (x.lab_grade[i] < 0 || x.lab_grade[i] > 25) return 0;

What is this? Are we comparing chars or ints here?

**Sebastiani** · 01-18-2003

Look, isdigit() is for chars, not ints. decimal 48 == '0'. decimal 57 == '9', get it? Better post some more code.

**JoeSixpack** · 01-18-2003

>someone types in values in an integer array.
i use a loop and go through each element and check if its a digit.<

Then you're duplicating effort already built into the C++ stream classes. Input the digits and test the stream state.

**mackol** · 01-18-2003

Originally posted by Sebastiani
Look, isdigit() is for chars, not ints. decimal 48 == '0'. decimal 57 == '9', get it? Better post some more code.

here is the small lab

www.mdofit.com/labs/27/lab2.cpp

i realized it is for character testing but then how to make sure that ppl dont input characters when i ask for ints..
and with the do while loop i have, (in my other function named getStudentData ) if i enter a character when an int is required it just goes on cout'ing forever..

the program works and all
i just want to make it full proof

**mackol** · 01-18-2003

Originally posted by Sebastiani
>> if (x.lab_grade[i] < 0 || x.lab_grade[i] > 25) return 0;

What is this? Are we comparing chars or ints here?

sorry.. that was just another check i had to make so i added that on into my code

**Sebastiani** · 01-18-2003

IMHO, you should validate the data BEFORE it even reaches class data. A good input procedure will solve that. For instance:

Code:

bool GetInt(int& value, ifstream& in = cin){
 char buff[256];
 in.getline(buff, 256);
 char * p = buff;
 value = 0;
     while(*p && *p != '\n')
  {
        if( !isdigit(*(p++) )  )
     {
        return false;
     }
  }
 value = atoi(buff);
 return true;
}

**mackol** · 01-18-2003

i have just been in my first ever C++ class for 2 weeks now so we havent yet gotten to
in.getline (though i can see what it does)
i understand what the method getline would do
but i dont understand the functions parameters

that is
ifstream& in = cin

the rest i understand

if u could just clarify this
thanks

**Sebastiani** · 01-18-2003

Those are just default parameters meaning that, if no file stream is supplied, cin is assumed. "in" is just an alias for whatever that stream may be called, it could just as well be called
ifstream& mackol, and of course that could be a file stream too, but to be fair, that function is not optimal for file input, and would probably have to be modified before doing so...

A simplified example of it's use might be:

Code:

int array[5];
int i = 0;

cout << "Please enter 5 values." <<endl;

      while(i < 5)
   {
     cout << "Enter a valid integer" <<endl;
          
          if( !GetInt(array[i]) )
       {
          cout << "Invalid input." <<endl;
          continue;
       }
     
    ++i;
   }

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