CS 107 - Lab 3

Boolean Expressions

A Boolean expression results in a Boolean value. A Boolean value can have one of two values: true or false. There is also a Boolean data type where you can store a Boolean value in a variable. The C++ keyword for a Boolean type is bool.

Boolean expressions are used in a program to decide if something should or should not be done. There are two main sets of operators that work with Boolean expressions:

Relational Operators
Boolean Operators

The relational operators take two values and evaluate to true or false based on the relation of the two values. There are six relational operators.

Name Symbol C++ Example Meaning
Equal to == val1 == 10 true if val1 is equal to 10, false otherwise
Not equal to != val1 != 10 true if val1 is not equal to 10, false otherwise
Greater than > val1 > 10 true if val1 is greater than 10, false otherwise
Greater than or equal to >= val1 >= 10 true if val1 is greater than or equal to 10, false otherwise
Less than < val1 < 10 true if val1 is less than 10, false otherwise
Less than or equal to <= val1 <= 10 true if val1 is less than or equal to 10, false otherwise

Name	Symbol	C++ Example	Meaning
Equal to	==	val1 == 10	true if val1 is equal to 10, false otherwise
Not equal to	!=	val1 != 10	true if val1 is not equal to 10, false otherwise
Greater than	>	val1 > 10	true if val1 is greater than 10, false otherwise
Greater than or equal to	>=	val1 >= 10	true if val1 is greater than or equal to 10, false otherwise
Less than	<	val1 < 10	true if val1 is less than 10, false otherwise
Less than or equal to	<=	val1 <= 10	true if val1 is less than or equal to 10, false otherwise

The Boolean operators take two Boolean values and evaluates to ture or false based on the definition of the operator. There are three Boolean operators.

AND
Symbol: &&
An AND operation evaulates to true if both of the operands are true; otherwise it evaluates to false. The following truth table shows how AND is defined:

val1 val2 val1 && val2
true true true
true false false
false true false
false false false
OR
Symbol: ||
An OR operation evaulates to true if at least one of the operands is true; otherwise it evaluates to false (when both of the operands are false). The following truth table shows how OR is defined:

val1 val2 val1 || val2
true true true
true false true
false true true
false false false
NOT
Symbol: !
A NOT operation evaluates to the opposite Boolean value of the operand. If the operand is true, the operation evaulates to false. If the operand is false, the operation evaluates to true. NOT is a unary operator (takes only one operand) instead of a binary operator (takes two operands) like AND and OR. The following truth table shows how NOT is defined:

val1 ! val1
true false
false true

val1	val2	val1 && val2
true	true	true
true	false	false
false	true	false
false	false	false

val1	val2	val1 \|\| val2
true	true	true
true	false	true
false	true	true
false	false	false

val1	! val1
true	false
false	true

Selection Statements

The primary selection statement is an IF statement. The IF statement can have a number of different forms. We will discuss three of them here: the IF-THEN statement, the IF-THEN-ELSE statement and the NESTED-IF statement.

The IF-THEN statement
The general form of an IF-THEN statement is:
```
     if ( cond )
         statement;
```
where:

if is the C++ keyword to specify the IF statement
cond is an Boolean expression
statement is a C++ statement that will be executed if the Boolean expression cond evaluates to true

The IF-THEN-ELSE statement

The general form of an IF-THEN-ELSE statement is:

     if ( cond )
         statementA;
     else
         statementB;

where:

if	is the C++ keyword to specify the IF statement
cond	is an Boolean expression
statementA	is a C++ statement that will be executed if the Boolean expression cond evaluates to true
else	is the C++ keyword to seperate statementA from statementB
statementB	is a C++ statement that will be executed if the Boolean expression cond evaluates to false

The NESTED-IF statement

A NESTED-IF statement is simply an IF-THEN-ELSE statement that has another IF statment for its statementB. This can be repeated as many times as desired. The general form of an NESTED-IF statement is:

     if ( cond1 )
         statementA;
     else if ( cond2 )
         statementB;
     else if ( cond3 )
         statementC;
     else if ( cond4 )
         statementD;
     else 
         statementE;

where:

if	is the C++ keyword to specify the IF statement
cond1, cond2, cond3, cond4	is an Boolean expression
statementA	is a C++ statement that will be executed if the Boolean expression cond evaluates to true
else	is the C++ keyword to seperate statementA from statementB
statementB	is a C++ statement that will be executed if the Boolean expression cond1 evaluates to false and cond2 evaluates to true
statementC	is a C++ statement that will be executed if the Boolean expressions cond1 and cond2 evaluate to false and cond3 evaluates to true
statementD	is a C++ statement that will be executed if the Boolean expressions cond1, cond2 and cond3 evaluate to false and cond4 evaluates to true
statementE	is a C++ statement that will be executed if the Boolean expressions cond1, cond2, cond3 and cond4 evaluate to false

Lab Assignment

Due: By your Lab Time during the fourth week of the semester (the week of 2/3/2003).

You may turn in the assignment to your TA during lab or place it in his mailbox in 905 SEO. It is suggested that you place it in his mailbox just in case you are unable to attend lab. Hand in a print out of your program to do the folliwng to your TA.

Create a c++ program on your UIC icarus account that will calculate the income taxes owed based on the following table.

Income Range Income Tax Amount
$0 - $2,000 Nothing
$2,001 - $20,000 4% * Each dollar earned over $2,000
$20,001 - $40,000 $720 + 8% * Each dollar earned over $20,000
$40,001 - $80,000 $2,320 + 16% * Each dollar earned over $20,000
$80,001 - $120,000 $8,720 + 24% * Each dollar earned over $20,000
$120,001 + $18,320 + 32% * Each dollar earned over $20,000
Your program is to prompt the user for their income amount and then read in this value from the input. Next your program should calcuate and output the the amount of income tax. Be sure to output your information is some readable style.

Income Range	Income Tax Amount
$0 - $2,000	Nothing
$2,001 - $20,000	4% * Each dollar earned over $2,000
$20,001 - $40,000	$720 + 8% * Each dollar earned over $20,000
$40,001 - $80,000	$2,320 + 16% * Each dollar earned over $20,000
$80,001 - $120,000	$8,720 + 24% * Each dollar earned over $20,000
$120,001 +	$18,320 + 32% * Each dollar earned over $20,000

Hand in a print out of your program to your TA.