operators, expressions and assignment
DESCRIPTION
Operators, Expressions and Assignment. Calculating Things. Expressions. Expressions are used to calculate values: 8 * 922 - 13 These values are often loaded into variables: X = 8 * 9Y = 22 - 13 Variables can be used in Expressions: X = 8 * YZ = X - 13. One Value Per Variable!. - PowerPoint PPT PresentationTRANSCRIPT
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Operators, Expressions and Assignment
Calculating Things...
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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
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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.
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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.
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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.
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Math Operators in Visual Basic
^ Power (Exponentiation)* Multiplication
/ Division (that rounds)
\ Division (that truncates)
Mod Modulo (Remainder)
+ Addition
- Subtraction
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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.
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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
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Question:
What is the operator for Exponentiation? A. * B. ^ C. ** D. ~ E. None of the above.
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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.
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Long Division
15 9 5 4
This is the Remainder
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Order of Precedence of Operators
( ) Parenthesis^ Exponentiation- Negation* / Multiplication, Division\ Integer DivisionMod Modulo+ - Addition, Subtraction
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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.
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Something a little more complicated
M=3/Y+2*Z^X\2-4Mod7*-3^(5*.2)
HUNH??????????
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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
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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
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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
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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.
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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.
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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
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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.
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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
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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
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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
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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
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Logical Operators
There are three logical operators:And Or Not
Used to combine comparison and logical expressions for more complex situations.
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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
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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”
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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
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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
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Values of Logical Expressions
Logical expressions return either True or False, no matter how complex they become.
TrueFalse
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Checking for correctness?
Perform operations by handCompare AnswersRepeat
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Example Programs
Evaluating an EquationThe quadratic formula:
y b b aca 2 42