Creating Simple Calculator

OBJECT ORIENTED PROGRAMMINGFINAL PROJECT

Fiona Angelina© 2011

Step 1: Creating the Design

Step 2: Make Sure All Buttons is Working

• Concatting Numbers

Simplest Way of Concatting Number

• Treat the number as a String. Cast to Double when calculating.

• Pseudocode://Get text from textfield, put it into String s//Concat s with other number (0, 1, 2, …, 9)//Set textfield with s

Simplest Way of Concatting Number

• Code might look like this:String s = text.getText();s = s.concat(“1”);text.setText(s);

Step 2: Make Sure All Buttons is Working

• Clear button

Clearing TextField

• To clear textfield, simply set it with a new value. In this case, it is “0”.

• Code might look like this:text.setText(“0”);

Step 2: Make Sure All Buttons is Working

• Backspace button

Allowing Backspace

• Use method subSequence with start index = 0 and end index = length of string – 1.

• Don’t forget to convert the resulting CharSequence to String.

• Code might look like this:String s = text.getText();CharSequence res = s.subsequence(0, s.length() – 1);

text.setText(res.toString());

Step 3: Operations

Strategy To Make Operation Works

• Strategy:– Create two variables:• operator: to store the last operator• operand: to store the last operand

How Does It Work?

• 1: After finished concatting number, user clicks “+”.

This button is clicked

How Does It Work?

• 2: Identify if it is the first number that user enters or not. Assume it is the first number, simply put the operand and operator inside the variables.

operator = “+”

operand = 98

How Does It Work?

• 3: User concats another number, and press “*”.

This button is clicked

How Does It Work?

• 4: Identify if it is a first operand or not. Now it is not the first operand. Therefore you have to calculate a result.

How Does It Workoperator = “+”operand = 98 newNum = 6

operand = 104

operator = “*”operand = 104

CURRENT STATUS

How Does It Work?

• 5: Suppose user concats another number, and this time press “=“.

This button is clicked

How Does It Work?

• 6: When user enters “=“ instead of other kind of operators, you have to calculate the result, and reset all the variables.

How Does It Work?

operator = “*”operand = 104 newNum = 3

operand = 312Output the result to textfield

operand = null operator = null

CURRENT STATUS

Step 4: Playing with Memory

• Strategy:– Create 1 null variable to represent the memory.– M+ & M- : identify if it is the first memory. If it is,

store the current value. If not, increment/decrement with the previous value.

– MC : set the memory to null.– MR : set textfield with value inside memory.