[Enigmatic Entity]

Hi everyone, I'm currently doing a novice java course, and I wish to ask the user to enter some integer. The problem is, I want the question to repeat if the user enters any letters in the field. At the moment it only repeats if the user enters <0 or >1452. Any letters will cause an input error. The solution needs to be simple using language "relevant" (i.e. simple) to the course. Any help greatly appreciated,

E.E.

[The E]

I'm assuming you are using integer.parseInt() to get the users' input, correct? If so, you could encapsulate that in a try/catch pair, since integer.parseInt() throws a NumberFormatException when confronted with something that isn't an integer.

But then, I guess that exception handling hasn't been discussed yet, has it?

[Enigmatic Entity]

Code: [Select]

Using a scanner object as well.

final int AGE_LO = 0, AGE_HI = 1452;
int age;

do
        {
        System.out.print("Age in months? (Rounded to nearest month between 0 and 1452): ");
        age = sc.nextInt();
        sc.nextLine();
        }
        while(age < 0 && age > 1452);

That's a sample of the loop I'm using. I was wondering if there is a way to check for letters/numbers without having to use a String and then check for 1, 2, 3, 4, 5, ...etc. or a, b, c, ....etc.
using a new command for each check, i.e. perhaps something like

if
{
        ageString.charAt(0) > 9

or similar. We haven't covered exception handling yet, sorry I can't use your suggestion, The E. Thanks for the reply, though.

[portej05]

The simplest way I can think of (without trying to be clever) is the following:

Code: [Select]

while ( true )
{
  readLine;
  if (line contains only numbers)
    break;
};


[Enigmatic Entity]

I've tried this, but I can see it's going to get messy:

Code: [Select]

final char AGE_L = '0', AGE_H = '1', AGE_9 = '9';
        String ageAns;
        char ageChar1;
        char ageChar2;
        char ageChar3;
        char ageChar4;
        int ageLength;
       
       
        do
        {
        do
        {
        do
        { System.out.print("Age in months? (Rounded to nearest month between 0 and 1320): ");
        ageAns = sc.next();
        ageChar1 = ageAns.charAt(0);
        ageChar2 = ageAns.charAt(1);
        ageChar3 = ageAns.charAt(2);
        ageLength = ageAns.length();
        }
        while(ageLength <= 3 && ((ageChar1 < AGE_L && ageChar2 < AGE_L && ageChar3 < AGE_L) || (ageChar1 > AGE_9 && ageChar2 > AGE_9 && ageChar3 > AGE_9)));
        }
        while(ageLength > 3 && (ageChar1 < AGE_L || ageChar1 > AGE_H));
        }
        while(ageLength > 4);


I think that a for loop using charAt and "++" my be an alternate method...

[portej05]

 

You probably should declare some functions like this:

Code: [Select]

bool isNumber( char c )
{ return ( '0' <= c && c <= '9' ) }

and then

Code: [Select]

bool isNumericString( String str )
{
  for ( int i = 0; i < str.length( ); i++ )
  {
     if ( !isNumber( str.charAt( i ) ) )
        return false;
  }

  return true;
}


[Hippo]

or

Code: [Select]

if( isAlpha( foo ) )

[portej05]

or

Code: [Select]

if( isAlpha( foo ) )

That, of course, is the other approach to the problem 

[Flipside]

I suppose that's one of the beauties and pains of Java, it's a bottomless toolbox, which is brilliant if you are faced with a 4-dimensional phased plasma grill with Base-6 encoding, but can make it a devil to find the damn screwdriver

[DragonClaw]

Here you go.

Code: [Select]

final int AGE_LO = 0, AGE_HI = 1452;
int age = -1;

System.out.print("Age in months? ");
while(age < AGE_LO || age > AGE_HI) {
System.out.print("Round to nearest month between 0 and 1452): ");
String line = sc.nextLine();
try {
age = Integer.parseInt(line);
} catch(Exception e) {
System.out.println("Invalid input, please enter an integer.");
}
}


[chief1983]

PHP is worse for that, there are many functions that do seemingly the same thing, sometimes though, with their arguments in a different order.  Also, many coders simply choose the wrong tool for the job, especially with PHP.  There are three replace functions, ereg_replace, preg_replace, and str_replace.  str_replace works with static strings, preg is PCRE and ereg is another (slower) form of Reg ex.  For whatever reason, the guys I work with insist on using ereg for general string replacement instead of str_replace (same with strpos() and ereg()).  There's also print() and echo(), only difference being that echo doesn't set a return.  The lack of consistency in the order of arguments for all those similar functions though is what annoys me the most.  It's like they never could decide if it should be (needle, haystack) or (haystack, needle).

[Enigmatic Entity]

I don't think we've learnt about "parseWhatever" yet, or !isNumber.

Code: [Select]

final int AGE_LO = 0, AGE_HI = 1320;
        char ageChar = ' ';
        int age, ageChk = 0, ageLength, ageCount = 0;
        String ageAns;



do
        {
        do
        {
        System.out.print("Age in months? (Rounded to nearest month between 0 and 1320): ");
        ageAns = sc.nextLine();
        ageLength = ageAns.length();
       
        for(ageChk = 0; ageChk < ageLength; ageChk++)
        {
        ageChar = ageAns.charAt(ageChk);
       
        if(ageChar < '0' || ageChar > '9')
        ageCount++;
        }
        }
        while(ageCount != 0);
       
        age = sc.nextInt();
        System.out.println(age);
        }
        while(age < 0 || age > 1320);

This works better, but stuffs up on letters only. There are some new errors elsewhere that are really annoying me at the moment, mainly:

javaFile.java:332: while expected
    }
     ^
javaFile.java:335: reached end of file while parsing

Process completed.

The first one is the end of the main() method!!! Why does it need a while loop? The other one is not understandable...

EDIT: I forgot a bracket in a for loop. Also, I discovered today that I didn't need to have all the check for correct values code, all it needed to do was accept and not analyse the "proper" input!

I did have a nice time trying the for loop, which worked for some inputs, but...mabye next time I won't need to attempt something that is so complicated. I have a habit of doing that.

[Flipside]

Building a nest makes your problems grow up faster

[BS403]

I had to do basically this same thing a little bit over a year ago before I learned about exceptions.  We had a simple way to do it, let me see if I can find my old code.

[Enigmatic Entity]

Oh, and just before I finished mine, I discovered someone's fully completed assignment on another forum. That seems a bit silly...I probably should have used more final variables, but there wasn't enough time left, so all the extraneous code was still there. A nice surprise if the marker accidentally entered the wrong values!