Doing Basic Math
In this program you use a constant and some methods from the Math class to calculate some math formulas. You ask the user for a number, and then you calculate 6 quantities that depend on that number. Finally, you print out the results of these calculations. You do all of this in the method 'calculateValues()'. You also make one small change to 'main(String args)' -- adding a question inside the double-quotes in this line:
input = JOptionPane.showInputDialog("");
In 'main()' you ask the user for a number, and you then calculate 6 quantities that are based on that number. You will need 6 local variables in 'calculateValues()' to store:
Use descriptive names like 'circleArea' for these 6 variables. This helps you and anyone else who looks at your program to understand what is going on. Here is how you would create the variable 'circleArea' inside 'calculateValues()':
To use the math constant π, use 'Math.PI'. Other math constants are also available.
To take the square root of 'number,' use 'Math.sqrt(number)'. To find a number like e3, use 'Math.exp(3)'. To calculate 34, use 'Math.pow(3, 4)'.
After calculating each of the 6 values listed above, add a line of descriptive output to a String. For example, in my program I first declared a String:
The first line of descriptive output looks like this:
msg = msg + "Number: " + f.format(number) + "\n";
or like this:
msg += "Number: " + f.format(number) + "\n";
Finally, after adding output for all 6 numbers, print out 'msg' in this way:
Here is the box that pops up at the end of my program if I enter '10' as the number:
I left this line in 'calculateValues()':
number = Math.abs(number);
This line uses the absolute value function to make sure that if the user enters a negative number, it is converted to positive before it is used.
To use Math methods like 'Math.pow()' and 'Math.sqrt(),' and Math constants like 'Math.PI,' you will need to add this line to the top of your program:
If you want to get a little fancy and set the number of decimal digits that print to 2, add this code to 'calculateValues()':
NumberFormat f = NumberFormat.getNumberInstance();
Then whenever you print out a 'double,' put that variable inside 'f.format()'. For example, if you have a 'double' called 'mpg,' this line would cause 'mpg' to print with 2 decimal digits:
System.out.println("Miles per gallon: " + f.format(mpg) );
You also have to add the line 'import java.text.NumberFormat;' at the top of the program.
You can download BasicMath.java to use as a starting point in writing your program.
To see how the program runs when it is done, you can download CompletedBasicMath.jar. Depending on which browser you are using, the program may run if you choose 'Open'. If not, you will have to select 'Save'. After the file downloads, double-click it and the completed program should run. (The file extension may change from .jar to .zip during the download. If this occurs, either while downloading or after downloading rename the file and change the file extension back to .jar.)