Input output

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Input - Process - Output

VB.NET

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Objectives

Distinguish between logic and syntax

Understand and use the input statement

Understand and use the assignment statement

Understand and use the output statement

Understand and use arithmetic operators with precedence

Successfully write program solutions that require input, processing, and output

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Logic and Syntax

A computer program is a solution to a problem.

An algorithm is the logical design used to accomplish a specific objective.

Syntax refers to the specific rules of a programming language.

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Input Statements

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Input Statements

An input statement accepts data from the user and stores that data into a variable.A variable is a storage location that can be accessed and changed by developer code.A variable has a name and an associated data value.A variable has a data type that determines the kind of data values the variable can store.

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Declaring Variables

Variables are declared with the Dim statement (short for Dimension statement).

One or more variables can be declared with a single Dim statement.

The Dim statement can be used to specify the variable’s initial value by placing an equal sign after the data type.

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Naming Rules for VariablesA variable must have a unique name, called an identifier.

Identifiers must follow three rules: Begin with a letter or underscore Contain only letters, digits, and underscores Cannot be reserved words

Dim identifier [, identifier] [As datatype [= initialvalue]]

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Working with Constants

A constant is a storage location whose value cannot change during the execution of the program e.g. VAT

Constants are declared with the Const declaration.

Const identifier As datatype = value

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Data TypeData Type Description

String Text

Byte (1 byte) Positive Whole Number (0 to 255)

Short (2 bytes) Whole Number (-32,768 to 32,767)

Integer (4 bytes) Whole Number (+ or – up to 2 million)

Long (8 bytes) Whole Number (huge!)

Single (4 bytes) Floating point (+ or – up to 3.4 x 1038)

Double (8 bytes) Floating point (+ or – up to 1.8 x 10308)

Decimal Stored exactly as BCD (currency & percentages)

Date Also stores time

Boolean True or false

Char Single character or positive number (up to 65535)

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Weekly Paycheck Program

The weekly paycheck program has two input variables:

Hours and Rate

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Operators and Expressions

An operator is a symbol that indicates an action to be performed.

Value-returning code elements such as variables, constants, and expressions can be combined with one or more operators to form an expression.

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Assignment Statements

The assignment statement can be used to perform a calculation and store the result.An expression is a value-returning code element, such as a variable or mathematical formula.

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The Assignment Statement

An assignment statement is used to store a value into a variable or an object property. variable = expression object.property = expression

The equal sign (=) is the assignment operator.

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Numbers and String Operators

Arithmetic operators require numeric operands and produce numeric results.

The string operator concatenation (&) requires String operands and produces a String result such as: S = “sun” & “set” S becomes “sunset”

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Numerical Operators

Operation Operator Expression 1 Result 1 Expression 2 Result 2

Plus & Minus + – 4 – 5 + 2 1 4 – (5 + 2) -3

Multiply & Divide * / 1 + 3 * 7 22 17 / 3 5.667

Integer Division \ 12 \ 4 3 17 \ 3 5

Integer Remainder Mod 12 Mod 4 0 17 Mod 3 2

Exponent (Power of) ^ 5 ^ 2 + 1 26 5 ^ (2 + 1) 125

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Output Statements (flow chart)

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Intrinsic Functions

VB .NET provides a large number of intrinsic functions to improve developer productivity.

Intrinsic functions support a broad range of activities, including math calculations, business calculations, time and date functions, string formatting functions, and many more.

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Common FunctionsIntrinsic functions are predefined commands that provide developers with common functions.

Function Example 1 Result 1 Example 2 Result 2

Val() (“23.5”) 23.5 (“£32”) 0

IsNumeric() (“23.5”) True (“£32”) True

FormatCurrency() (1234.567) £1,234.57 (4.5) £4.50

Format(expr,str)(1/2,

“0.##”) “0.5”(6.666,

“0.###”) “6.67”

Int() (3.8) 3 Int(Rnd()) 0

Rnd() ()Double value

between 0 and 1 Int(Rnd()*6)+1Integer

from 1 to 6

Abs() Import System.Math

(-3.3) 3.3 (5.67) 5.67

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Rnd Statement

The Rnd statement generates a single precision random value between 0.0 up to (but not including) 1.0.

The Randomize statement is used to change the seed value (random sequence).

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SummaryVariables are storage locations used for holding input and processing information. Each variable has two components: its name and its value. It is good practice to make variable names descriptive with

mixed case. The Dim statement is used to declare a variable by

specifying its name and data type.

Input statements are used to get data into variables.

Assignment statements are used to perform calculations and store the result.

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Summary

Expressions are combinations of operators and value-returning code elements such as variables, constants, and literals. One of the common uses of an expression is to perform

a calculation for an assignment statement. Intrinsic functions provide pre-defined methods for

common processing requirements.

Output statements are used to display information.Input, assignment, and output statements are sufficient to write small programs.