problem: calculator not working

[Albert Park]

Hello everyone,

I was messing with calculator problem in introduction to java programming text.
When I have string arrays in A class and call the exercise class to have string variables to convert to char, everything works fine.
So i decided to try passing char arrays to exercise class thinking that it may be easier to pass char variables without conversion.
It works except that the result i am getting is all wrong. For example 1 + 3 comes out as 100.

Any idea what i am doing wrong??

Thanks in advance.

public class A {
	public static void main(String[] args){
		
		char[] chars = {'1', '+', '3'};
		
		exercise.main(chars);
	}
}

class exercise{
	public static void main(char[] args){
		
		if (args.length != 3){
			System.out.println("Calculator terminated");
		System.exit(0);
		}
		
		int result = 0;
		
		switch (args[1]){
		case '+' : result = (args[0]) + (args[2]);
		break;
		
		case '-' : result = (args[0]) - (args[2]);
		break;
		
		case '*' : result = (args[0]) * (args[2]);
		break;
		
		case '/' : result = (args[0]) / (args[2]);
		break;
		}
		System.out.println("The result of " + args[0] + " " + args[1] + " " + args[2] + " = " + result);
		}
	}

[Steve Luke]

The char '1' is not the number one, it is a numeric character code used to represent the character '1'. You still need to convert from char to int.

[Albert Park]

Steve Luke wrote:The char '1' is not the number one, it is a numeric character code used to represent the character '1'. You still need to convert from char to int.

Thanks Steve. hmm.. then when I convert from string to char and pass on string arrays, why does it give me a correct answer?

[Steve Luke]

Dunno, show the code

[Albert Park]

Here you go.

public class A {
	public static void main(String[] args){
		
		String[] strings = {"3", "+", "5"};
		
		exercise.main(strings);
	}
}

class exercise{
	public static void main(String[] args){
		
		if (args.length != 3){
			System.out.println("Calculator terminated");
		System.exit(0);
		}
		
		int result = 0;
		
		switch (args[1].charAt(0)){
		case '+' : result = Integer.parseInt(args[0]) + Integer.parseInt(args[2]);
		break;
		
		case '-' : result = Integer.parseInt(args[0]) - Integer.parseInt(args[2]);
		break;
		
		case '*' : result = Integer.parseInt(args[0]) * Integer.parseInt(args[2]);
		break;
		
		case '/' : result = Integer.parseInt(args[0]) / Integer.parseInt(args[2]);
		break;
		}
		System.out.println("The result of " + args[0] + " " + args[1] + " " + args[2] + " = " + result);
		}
	}

[Steve Luke]

I just checked the character codes for digits (http://www.unicode.org/charts/PDF/U0000.pdf). '1' is 0x0031, and '3' is 0x0033. Add them and you get 0x0064 which in decimal (those are hex numbers) comes out to be 100 - which is what your calculator is getting.

[Albert Park]

ok. nvm. I did convert from string to int.

Thank you.

[Albert Park]

one more question,

is line 11 (args[1].charAt(0)) from exercise class necessary?
what is the reason for converting to char instead of leaving it as string?

[Steve Luke]

Albert Park wrote:one more question,

is line 11 (args[1].charAt(0)) from exercise class necessary?
what is the reason for converting to char instead of leaving it as string?

I don't think it is necessary any more - try running without it. The reason is that until Java 7 (I think) you couldn't run a switch on a String, only on enums and on primitives - and chars are primitives. I may be wrong about Java 7 tho, so give it a try and see if it works now without the conversion.

[Albert Park]

Steve Luke wrote:

Albert Park wrote:one more question,

is line 11 (args[1].charAt(0)) from exercise class necessary?
what is the reason for converting to char instead of leaving it as string?

I don't think it is necessary any more - try running without it. The reason is that until Java 7 (I think) you couldn't run a switch on a String, only on enums and on primitives - and chars are primitives. I may be wrong about Java 7 tho, so give it a try and see if it works now without the conversion.

oh ic. yea, like you said it does work with String. Makes more sense now. Thank you.