Operators, Expressions and Assignment

Operators, Expressions and Assignment

Calculating Things...

Expressions

Expressions are used to calculate values:

8 * 9 22 - 13 These values are often loaded into

variables:X = 8 * 9 Y = 22 - 13

Variables can be used in Expressions:X = 8 * Y Z = X - 13

One Value Per Variable!

Variables hold a single value. A variable can occur on both sides of an

equation:X = X + 1

Y = Y * X / (7 - Y) This means:

take the value out Use it to calculate the new value. Put the new value in the variable.

Expressions and Operators

Expressions are built up using operators and operands.

Depending on the operators used and the purpose of the expression, they fall into three general groups: Mathematical Comparison Logical

These types may be mixed.

Kinds of Expressions

Mathematical Expressions Used to calculate values.

Comparison Expressions Compare two values and evaluate a

relationship between them. Logical Expressions

Combines comparison expressions.

Math Operators in Visual Basic

^ Power (Exponentiation)* Multiplication

/ Division (that rounds)

\ Division (that truncates)

Mod Modulo (Remainder)

+ Addition

- Subtraction

Why two operators for division?

Most languages have one, and it truncates the value given it. Truncation means removing any fractional

part from a number.5.5 -> 53.423 -> 3

VB has the truncating division (backslash) to be consistent with other languages. This is known as integer division.

The VB Division

VB has a rounding division (forward slash) to be consistent with your expectations.

In almost every circumstance you’ll want to use the forward slash operator.

7 / 8 -> 18 / 5 -> 2

Question:

What is the operator for Exponentiation? A. * B. ^ C. ** D. ~ E. None of the above.

What is Modulo?It gives the remainder of a division operation.You can calculate it for yourself like this:

X mod Y => (X / Y - Floor(X / Y)) * YOr, you can remember long division.

Long Division

15 9 5 4

This is the Remainder

Order of Precedence of Operators

( ) Parenthesis^ Exponentiation- Negation* / Multiplication, Division\ Integer DivisionMod Modulo+ - Addition, Subtraction

Examples of Math Expression

X = 1 + 1 The value 2 is loaded into variable X

Y = X * 2 The value in X is multiplied by 2 and the result is

loaded into Y, so Y will hold 4. Z = X * 3 + Y ^ 2

The value in Y is raised to the power 2. The value in X is multiplied by 3. The results are added and loaded into Z.

Something a little more complicated

M=3/Y+2*Z^X\2-4Mod7*-3^(5*.2)

HUNH??????????

Step by Step

Given: X = 2, Y = 4, and Z = 10M = 3 / Y + 2 * Z ^ X \ 2 - 4 Mod 7 * -3 ^ (5 * .2)

Parenthesis: (5 * .2) => 1.0M = 3 / Y + 2 * Z ^ X \ 2 - 4 Mod 7 * -3 ^ 1

Exponentiation: Z ^ X => 100, -3 ^ 1 => -3M = 3 / Y + 2 * 100 \ 2 - 4 Mod 7 * -3

Step by Step by Step

M = 3 / Y + 2 * 100 \ 2 - 4 Mod 7 * -3Now do the division and multiplication, left to

right: 3 / Y => .75, 2 * 100 => 200, 7 * -3 => -21

M = .75 + 200 \ 2 - 4 Mod -21

Step by Step by Step...

M = .75 + 200 \ 2 - 4 Mod -21 Then the Integer Division: 200 \ 2 => 100M = .75 + 100 - 4 Mod -21Then the modulus operator: 4 Mod -21 => 4M = .75 + 100 - 4

Step by Step by Step...

Finally, do the addition and subtraction left to right: .75 + 100 => 100.75, 100.75 - 4 => 96.75

M = 96.75So the answer is 96.75, which is loaded

into variable M.

Question:

What value will be loaded into Z from the following expression.

Z = 6 + 8 / 2 ^ 2 A. 49 B. 8 C. 32 D. 3.5 E. None of the above.

Comparison Operators There are six basic comparison operators

< Less Than> Greater Than<= Less Than or Equal To>= Greater Than or Equal To= Equal To< > Not Equal To

Something you don’t have to know!

There are two esoteric comparison operators:Like Compares StringsIs Compares Objects You’re not responsible for knowing these

and we’ll not be covering them.

Use of Comparison Operators

Comparison Operators ask questions:Is X bigger than Y?: X > YIs Y at least as large Z?: Y >= ZIs X the same as Z?: X = Z

Values Returned

Comparison operators all return one of two values: True or False.

Either the relationship holds or it doesn’t Either a > b, so the result is True or a isn’t greater than b and the

result is False

Representing True & False

True is represented in VB as -1 Which is 11111111 in binary

False is represented in VB as 0 Which is 00000000 in binary

Question:

If I want to know if X is greater than 5, I would use: A. X = 4.9 B. X>= 5 C. X < 5 D. X <> 5 E. None of the above

Logical Operators

There are three logical operators:And Or Not

Used to combine comparison and logical expressions for more complex situations.

Use of Logical Operators

To enroll at WSU you must have a high school diploma and have lots of money:

HighSchool = “Yes” And Money > $1000

More Logical Operators To graduate from WSU you must have

135 credits, an acceptable GPA and a be enrolled in a college:

Credits >= 135 And GPA > 2.0 And Not

College = “None”

Credits >= 135 And GPA > 2.0 And College <> “None”

Still More Logical Operators

To pay for your Ultra Deluxe Slice-o-Matic in three easy payments you need either $120 in cash or a credit card.

CreditCard = “Yes” Or Cash >= 120

Question:

If I wanted to know if A is greater than B and that C is not greater than D I would use: A. A > B and C > D B. A > B and not C > D C. A > B and C <= D D. Answer B and Answer C E. None of the above

Values of Logical Expressions

Logical expressions return either True or False, no matter how complex they become.

TrueFalse

Checking for correctness?

Perform operations by handCompare AnswersRepeat

Example Programs

Evaluating an EquationThe quadratic formula:

y b b aca 2 42