If input is/is not a number

[Hnizdo]

Hello,
I've started learning java this semester in school and my level is still quite low.
Now i found a problem with my program:

I want the program to recognise whether the imput is a number, then it is saved into int variable. This part works correctly. I made the second part in quite the same way It is supposed to repeat the input again if it contains any non-digit characters, until it consists of digits only. This is how it works(or rather doesnt):

class test{

public static void main (String[] args){

String text = In.readLine();
char [] pole = text.toCharArray();
String number = "";
int cycle =0;



for (int i=0;i<pole.length;i++)
{
if (Character.isDigit (pole[i]))
{
number= number + pole[i];
}
else if (!Character.isDigit (pole[i]))
{
Out.print("No number entered, enter number");

}

}
int a = new Integer(number).intValue();
Out.print (a);

}
}

Any ideas how to make it work? I would prefere a way, that doesnt change it completelly, but there is no other, or reasonable way, it doesnt matter. Thank you for help.

[jkmyoung]

So you want the first 8 characters of the line to be digits? There's a couple methods involving putting a loop around most of your code.


1. Flag method: Put a while loop around most of your function.

boolean needNumber = true;
while (needNumber)
needNumber = false;
// your main code.
// input string.
// parse ...
 ...
  else if (!Character.isDigit (pole[i]))
  {
    Out.print("No number entered, enter number");
    needNumber = true; // reset so we have to enter again.
  }
 }// end for
}// end while
//convert and output number.

2. break method.
Put a while around the same part, but declare i earlier.:

int i = 0;
while (i<pole.length){
...
...
  else if (!Character.isDigit (pole[i]))
  {
    Out.print("No number entered, enter number");
    break; // break for loop
  }
 }//end for
}//end while

If we break unnaturally, then i<pole.length is still true.

Are you trying to add all the digits?

[Hnizdo]

I want to use it to determine whether the input is a number (all the chars are actually digits) or if it contains any/or only letters, like 8saf or asdf. In that case it
continue by making the new input as long as the user doesnt write digit only string.

[Hnizdo]

I did it like this, so far it seems to work, but I appreciate any ideas how to make it easier, shorter, better, anything helps.

class test{

public static void main (String[] args){


int i=0;
String text;
char [] pole;
String number = "";

while (i<1)
{ i=1;
text = In.readLine();
pole = text.toCharArray();
number = "";

for ( i=0;i<pole.length;i++)
{
if (Character.isDigit (pole[i]))
{
number= number + pole[i];
}
else if (!Character.isDigit (pole[i]))
{
Out.print("No number entered, enter number");
i=0;
break;
}

}
}
int a = new Integer(number).intValue();
Out.print (a);

}
}

[jkmyoung]

It's a little dangerous flagging i in that way, but it will work.
The i=1; is meaningless, as it promptly gets reset to i=0 at the for loop.

[Hnizdo]

I transformed the code a bit to be able to set certain borders, now I cannot think about any errors, that could happen. It looks like this:

class test{

public static void main (String[] args){


int i=0,a=1;
String text;
char [] pole;
String number = "";

while (i<1)
{ text = In.readLine();
pole = text.toCharArray();
number = "";
for ( i=0;i<pole.length;i++)
{
if (Character.isDigit (pole[i]))
{
number= number + pole[i];
a = new Integer(number).intValue();
if (a<1 || a>5000)
{
Out.print ("Out of range, enter number between 1 and 5000");
i=0;
break;
}
}
else if (!Character.isDigit (pole[i]))
{
Out.print("No number entered, enter number");
i=0;
break;
}
}
}


Out.print (a);

}
}


What was the danger you were talking about?

[Hnizdo]

and one more question: if I wanted to use it in a program, i suppose I should put it into a method, but I'm not really sure how it should look like and how should I call it. I have some experience with methods, not much though, but this one is weird since it transforms int and string and does not really have any variable which I should for example like

public static int condition (int num)

when I tried to do it like, and called it like number = condition(num) it didnt work.

Really thanks for your help