lecture 4 - variables, constants, and data types (1)

8/14/2019 Lecture 4 - Variables, Constants, And Data Types (1)

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Lecture 4: Variables, Constants,

and Data Types


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Outline

In this lecture, we will discuss:

Declaring and using Variables

Declaring Constants Common data types used in math

Integers and Doubles (floating point numbers)

Mathematical operations

Including operators and precedence

And Implement Two VB .NET Programs:

Simple Calculator Price Calculator


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Constants

Assigning a variable fixes a memory location for storage. However, within limits a variable may take arbitrary values

depending on the data type (i.e., Integer, Double, etc).

The value of a constant, on the other hand, is fixed.

The VB syntax for declaring a constant is:

Const const_nameAs Data_Type= value

Const is a keyword declaring the constant;

Const_nameand value are the name and value of the constant;

Data_Typeis the type of constant.

Note: variables can also be given initial values

This is called initialization.

Example: Dim x As Integer = 6

Declares Integer variable x, and sets its starting value to 6.

Some examples: Const x As Integer = 10

Const PI As Double = 3.14159265


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Data Types for Numbers

When working with numbers, we use two types of data: Integers (usually take the Integer type):

Example: 1, 2, 3,

Useful for discretemath: counting objects (cardinal)

Example: There were six customers.

ordering objects (ordinal)

Example: The one-hundredth customer will win

Floating point numbers (usually take the Double type):

Example: 1.50, 3.1415926, etc have a decimal point.

More useful for normalarithmetic.

Note: If you do not explicitly declare a variables data type

It is declared by the system as an Object, by default.

We will talk more about Integers and Floats, and other data

types, shortly First, lets look at some basic mathematical operations.


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Mathematical Operators

The table below contains the operators available for basic mathoperations:


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Program 4.1 - A Simple Calculator

Desired Functionality:

Make a simple program, to implement these operators


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Simple Calculator (cont.)


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Simple Calculator (cont.)


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Math Statements

In our previous example, we saw a math statement (C = A + B)

Question: what does the statement, x = x + 1 do?

Thinking in terms of arithmetic, this is a nonsense statement.

Since = is defined as equality But x is never equal to x + 1!

However, if we instead think in VB, it makes perfect sense!

Remember= is the assignment operator.

Thus, x = x + 1 tells the computer to: First, get the value stored in variable x.

Then, add 1 to this value.

Lastly, store the result in variable x.

For example, assume x starts out as 10:

Dim x As Integer = 10

x = x + 1

During run-time, the right side is first evaluated to yield 11.

Then, this result (11) is passed to the left side (x).

So, the overall result is to set: x = 11.


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Assignment Operators

Simple one-variable expressions, such as:

n = n + 1

Are really assignment operations, Which involve the simple updating of the variable

Short-hand operators exist for such operations:

Which combine both operators into a single assignment operation.

For instance, the statement,

n = n + 8 can be written as: n += 8

Either form assigns the value n + 8 to the variable n.

Short-hand operators exist for all 4 basic operations: +=, -=, *=, /=


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Math Statements (cont.)

More generally, a math statement takes the form:

left_side = right_side

Where, left_side is a variable

While right_side is a mathematical expression.

At run-time, the right_side is evaluated

And then passed to the left_side.

For instance, as a result of the statement: z = 2 * 3

First, the right side is evaluated (yielding 6).

Then, the result is passed to z (setting z equal to 6).

What about a compound statement (sevaral math ops):

x = 3 * 2 + 1 ? If we perform the multiplication first, we get :

x = 6 + 1 = 7.

If we add first, we get :

x = 3 * 3 = 9.

Which is correct?


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Operator Precedence

In VB, the order of evaluation of math operators is determined byprecedence.

For arithmetic, the order of evaluation is (first to last):

Exponentiation (^) Unary identity and negation (+, )

Such as the - in x = -6

Multiplication and floating-point division (*, /)

Integer division ()

Modulus arithmetic (Mod)

Addition and subtraction (+, )

Note that operations on strings come next (more, later): String concatenation (+)

String concatenation (&)

So, for our example:

x = 3 * 2 + 1

= 6 + 1 = 7.


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Overriding Precedence

What if we want to do the addition first?

VBs default operation order can be over-ridden easily!

By simply adding parentheses.

In particular, operations enclosed by parenthesis are evaluated first

Examples:

Our example, stated as: z = 3 * (2 + 1) = 3 * 3 = 9

However, stated as: y = (3 * 2) + 1 = 6 + 1 = 7 Thus, parenthesis provide simple program control, during execution.

This also applies to nested parentheses

Parentheses inside of parentheses.

The most internal operations are performed first. Example: X = (((2 + 1) * 3) + ((7 + 6) 4)) * 5

= ((3 * 3) + (13 -4)) * 5

= (9 + 9) * 5

= 18 * 5= 90.

P P i C l l


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Program 2 Price Calculator

Lets make a program that allows us to:1. Name a product;

2. Assign it a price and a desired number to buy;

3. Calculate the subtotal, consumption tax, and total.

Assume a consumption tax rate of 5%.

It is easier to think in terms of: Variables and Calculations

Our Variables:

Input Data: price (a Double) and quantity (an Integer) Output Data: subtotal and total (both are Double type)

We also have a Constant: the tax_rate (a Double)

Our Calculations:

Compute the Subtotal

subtotal = price * quantity

Compute Consumption Tax

Consumption_tax = subtotal * tax_rate

Compute the Total

Total = subtotal + consumption_tax

Our Algorithm= Read the Input+ Compute each+ Display Results

P 2 ( )


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Program 2 (cont.)

So, in a more organized form, we have:

Const tax_rate As Double = 0.15


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Program 2 (cont.)


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Program 2 (cont.)


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Conclusion

In this lecture, we have discussed:

Declaration and Use of Variables Declaring Constants

Common Data Types for mathematics Integers and Doubles

Mathematical Operations arithmetic operators

assignment operators precedence

Algorithm Design

And Implemented two Programs, using Visual Studio .NET:A. Simple Calculator

B. Price Calculator

With the remainder of the lecture, you should practice: Try creating the programs yourself.

lecture 4 - variables, constants, and data types (1)

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