Programming Example: tax
computation
Introduction
• In this webpage, we will study a programming example
using the conditional statements (if and if-else) to write a
Java program to compute the tax owed.
Formula to compute the tax owed
• Decision diagram to compute taxes owed:
Formula to compute the tax owed (cont.)
• Example 1: someone single earning $40,000 pays:
• 15% of $21,450,
plus
• 28% of ($40,000 − $21,450)
Formula to compute the tax owed (cont.)
• Graphically:
Formula to compute the tax owed (cont.)
• Example 2: someone single earning $60,000 pays:
•15% of $21,450,
plus
•28% of ($51,900 - $21,450),
plus
•31% of ($60,000 - $51,900)
Formula to compute the tax owed (cont.)
• Graphically:
Formula to compute the tax owed (cont.)
• Algorithm:
Define the following constants:
S1 = 21450
S2 = 30450
M1 = 35800
M2 = 86500
Formula to compute the tax owed (cont.)
• Structure diagram:
Formula to compute the tax owed (cont.)
• Example input: status = 'S' and income = 40000
Formula to compute the tax owed (cont.)
• The tax computation algorithm in Java:
(The whole program is too large to show here).
if ( status == 'S' )
{ // ***** single
if ( income <= S1 )
tax = RATE1 * income;
else if ( income <= S2 )
tax = RATE1 * S1
+ RATE2 * (income - S1);
else
tax = RATE1 * S1
+ RATE2 * (S2 - S1)
+ RATE3 * (income - S2);
}
Formula to compute the tax owed (cont.)
else
{ // ***** married
if ( income <= M1 )
tax = RATE1 * income;
else if ( income <= M2 )
tax = RATE1 * M1
+ RATE2 * (income - M1);
else
tax = RATE1 * M1
+ RATE2 * (M2 - M1)
+ RATE3 * (income - M2);
}
Formula to compute the tax owed (cont.)
• Constants used in the program:
 RATE1 = 0.15
 RATE2 = 0.28
 RATE3 = 0.31
 S1 = 21450
 S2 = 51900
 M1 = 35800
 M2 = 86500
(Tax rate)
(Income brackets)
Formula to compute the tax owed (cont.)
• Java program:
import java.util.Scanner;
public class ComputeTax
{
public static void main(String[] args)
{
final double RATE1 = 0.15; // Tax rates
final double RATE2 = 0.25;
final double RATE3 = 0.31;
final double S1 = 21450.0;
final double S2 = 51900.0;
final double M1 = 35800.0;
final double M2 = 86500.0;
// Tax brackets for single
// Tax brackets for married
Formula to compute the tax owed (cont.)
char status;
double income = 0;
double tax = 0;
Scanner in = new Scanner(System.in); // Construct Scanner object
System.out.print("Enter status (S or M) = ");
status = in.next().charAt(0);
// Read in status
System.out.print("Enter income = ");
income = in.nextDouble();
// Read in income
>>>> Insert the Tax Computation Algorithm (see above) here <<<<
System.out.println("Tax = " + tax);
}
}
Formula to compute the tax owed (cont.)
• Programming advice:
• Using symbolic constants in computer program is
highly recommended because when the tax rates or
income brackets changes, we can easily
accommodate the changes by changing the values
of the constant definitions at the start of the
program.
• We don't have to search for the constants inside
the program !
Formula to compute the tax owed (cont.)
• Example Program: (The entire program is here)
– Prog file:
http://mathcs.emory.edu/~cheung/Courses/170/Syllabus/06/Progs/
ComputeTax.java
• How to run the program:
• Right click on link and save in a scratch directory
• To compile: javac ComputeTax.java
• To run:
java ComputeTax