Control Structures and Conditionals :3

Ft. Catherine, Nicole, Julia and Maria

Agenda for Today

• Attendance
• The If Statement
• Inequalities
• Boolean Operators
• Else
• If Structures
• Applications
• Challenge Problem

The If Statement

• Basis of all decision making in programming
• It’s like asking yes or no questions
• Controls the flow of the execution of the program
• Contains a block of code, only executed if the condition of the if statement is true

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Ex:

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The print statement will not execute since the condition in the if statement is false.

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For general use:

Inequalities

== (equality)

• Determines if two values are equivalent

!= (inequality)

• Determines if two values are not equivalent

> (greater than)

• Determines if the value on the left is greater than the value on the right

< (less than)

• Determines if the value on the left is less than the value on the right

>= (greater than or equal to)

• Determines if the value on the left is greater than or equal to the value on the right

<= (less than or equal to

• Determines if the value on the left is less than or equal to the value on the right

Note About Inequalities

• The inequality symbols on the previous slide only work with primitive data types:
• int, char, float, boolean, etc. (only == and != work on boolean)
• This does not include Strings
• == will only compare if the Strings are stored in the same memory location
• To ensure that the Strings are compared properly, use the equals() method

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Instead of:

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Do:

Instead of:

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Do:

Boolean Operators

• Boolean operators (logical operators) are used to combine simple conditions into more complex expressions

&& (AND)

• True if both expressions are true
• False if either one is false

|| (OR)

• True if either expression is true
• False if both of them are false

! (NOT)

• Inverts/negates the Boolean value of an expression

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*You can find the key for OR above the enter key

Operator Precedence and De Morgan’s Laws

Order of precedence:

1. ! (NOT)
2. && (AND)
3. || (OR)
1. You can use parentheses to indicate precedence
2. It’s like BEDMAS for boolean operators

De Morgan’s Laws

They are:

1. !(A || B) = !A && !B
2. !(A && B) = !A || !B
1. A bit trippy at first but if you think really hard about it, they makes sense

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Boolean Operators Examples

If a = 5, b = 2, and c = 4, are the following true or false?

!(a != 4) && b > 0 || c >= 4 && a > b

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!(a != 4) && (b > 0 || c >= 4 && a > b)

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!(a != 4) && b > 0 || !(c >= b) && a > b

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(!(a != 4) || b > 0 || !(c >= b)) && a > b

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True

True

False

False

Else

• Can be used to extend an if structure
• If the condition is false, the statements after the keyword else will be executed
• Can be used as:
• Else if - to check another condition if the previous one was false
• Else - if all conditions are false, the program defaults to this

General Example:

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If Structures

• We can chain together a bunch of if-then-else statements to create a structure

Ex:

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Output:

a is greater than 3

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• Even though a can satisfy more than one expression, once a condition is met, it skips the rest of the if structure

This part is skipped because the previous condition was satisfied

Applications

Animation

• check if an object has reached a boundary

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Challenge Problem

Write a program that lists the numbers from 1 to 100, but:

• For multiples of 3, write “Fizz”
• For multiples of 5, write “Buzz”
• For multiples of both, write “FizzBuzz”