how to write a simple calculator code? Help!

JavaLost · #1 11-Oct-2006, 05:24

Hey, guys,

I am now have to write a java programm to implement a simple calculator of basic operations(addition, subtraction, multiplication and division) on integers.

The user may enter a string comprising an operand, a binary operator, and a second operand, with any number of space characters between them. There may be leading spaces and trailing spaces in the input.

If an invalid input is encountered, a message "Error in expression" is displayed and the calculation is skipped. Otherwise, the respective operation is carried out, and the result displayed. The user then enters another string. To end the calculation, the user enters 'q'.

I also have to handle division-by-zero error so that your program does not crash when it happens.

The operand is an integer. Examples of valid operands are 23, 0, -123, but not 23.5 (not an integer), 51.0 (not an integer), +123 (unary plus not accepted).

Anyone has idea about how to write this program??

Below , i attached a partial code for this program. Hope someone can help me with this program. Thanks a lot!

LuciWiz · #2 11-Oct-2006, 06:29

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Justin Fox · #3 24-Oct-2006, 01:41

i did a program almost exactly like this in my datastructures class...

except all we had to use is digits 0-9...

if i were you, i would definately use StringTokenizer...

you can set the delimiter to "+-*/"..

this mean when you call

JAVA Code:


String currToken = a.nextToken();

// where a is set up like so..

a = new StringTokenizer(userInput,"+-/*",true);

it not only accepts strings(substrings) separated by space characters,
but also any string separated by +,-,/ and *.

so what you can do is have a string that is called operators...

that is set up like so..

JAVA Code:


String operators = "+-/*";

and when you call StringTokenizer.nextToken() you know you're going
to get a integer or a operator(+.-,/,*).

so when you want to decide if it is a int or a operator try the following...

JAVA Code:


if(currToken.indexOf(operators) > -1) // index of return indexOf currToken
currToken = a.nextToken();              // relative to operators.
else                                              // if currToken isnt in operators, 
{                                                 // indexOf returns -1

// when you try to cast a string 
// to an integer, if the currToken isn't
// and int, it will throw an exception.

try{
  int a = Integer.parseInt(currToken);
    }
    catch(Exception e){System.out.println("invalid expression"); }

}

and if you have to paranthesis the expression....

just iterate through the string a see if the number of '(' and ')' are equal..

hope this stuff helps a lil...

the stringtokenizer should make it a lot easier on you...

and if you want to know if a certain char is a digit...

use Character.isDigit(char a);

Justin

to use StringTokenizer..

import java.util.StringTokenizer;

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how to write a simple calculator code? Help!

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