Thread: Help with calculator

Originally Posted by Norm

Looks like you are making progress. As I said in post#20, the index value needs to be adjusted so that the String does not have the "+"
For example use index+1 instead of just index as the argument to substring

Yes thank you! (tecken+1) only prints our the last number now.

Originally Posted by Norm

Yes that is all that should be in num2 - the second operand: "2"

Change the expression to something with values that will not be confused with index values. For example: "321+44"
The problem with "1+2" is that when 1 is printed, you do not know if it is the index of "+" or the value of the first operand.
When the second operand's value is printed, you should see "44" not "2"

I understand I changed my string to 341+44 and tecken+1 prints out 44 and 0, tecken prints out 321

Originally Posted by Norm

Ok, now the expression has been broken into three parts. Now convert the operands to int values and do the addition to get the results.

Okay

int num4 = Integer.parseInt(num2);
        int num5 = Integer.parseInt(num1);

What am I going to put in my print code?

Originally Posted by Norm

What do you want to see on the console when the program executes?

The result of what 341+44 is

Originally Posted by Norm

Ok, if those two values are in variables, can you add the variables together to get the desired result?

I tried making them into one string and convert it to int to print out but then it prints out 34144

String result = num1 + num2;
        int num4 = Integer.parseInt(result);
 
        System.out.println(result);

Originally Posted by Norm

Leave them as int values.
Use an assignment statement to assign their sum to another int variable.
Then print the value of that int variable.

The + operator with two Strings concatenates their values: "asd" + "def" gives "asddef"

okay what is assignment statement?

Originally Posted by Norm

A statement that assigns a value to a variable. The variable is on the left, followed by =, followed by a value
Examples from your code:
String result = num1 + num2;
int num4 = Integer.parseInt(result);
int tecken = num.indexOf('+');

See the tutorial: https://docs.oracle.com/javase/tutor...bolts/op1.html

like this?
int result = (num4 + num5);
System.out.println(result);

Originally Posted by Norm

Did you try that? What happened?

Yes it worked!! I only need now to make error messages when you try to /0 and if you try to use more than to numbers. So when you type in for example 2+2-1, you're supposed to get an error message. I've tried with 0 like
if (s.contains("/0")){
JOptionPane.showMessageDialog(null, "error");
}
but it doesn't work and for the other I don't know....

Originally Posted by Norm

Do you know about try{}catch for trapping exceptions? If so you could put the parseInt method calls inside of a try{}catch block and let the parseInt method throw an exception if either of the two operands (before and after the opcode) are not valid int values.

No I haven't learn about it yet and I'm not sure if my teacher will allow it but I'll ask him. So I can't use if statement or a for loop?

Originally Posted by Norm

Yes, you can make a method to scan a String and test if it contains only digits. The String class has methods for getting at each character in the String.
The Character class has methods to test a character to see if it is a digit.

okay something like this?

for (i=0; i<s.length(); i++)
			if (s.charAt(i) == '')

Originally Posted by Norm

The test inside of the if statement should be about the char being a digit or not. See the Character class for method to use.

okay I solved it like this

int count=0;

for ( int i=0; i<s.length(); i++) {
if (s.charAt(i) == '*' || s.charAt(i) == '/' || s.charAt(i) == '+' || s.charAt(i) == '-') {


count++;
}

} if (count > 1) {
System.out.println("error");
System.exit(0);
}

I missed making an error message if there is a letter, how do I make it?