Cycle Program Development Problem definition o Understand and define the problem o Involves determining the programs requirements and how they can be met Program Design o Carefully determine the steps the program has to go through Design the overall structure of the code Develop the procedure o Algorithm Flowchart Pseudocode o Does not involve writing instructions for the program o Choose the interface Program Coding o Use his/her knowledge of the programming language Syntax The set of rules that determine whether a particular statement is correctly formulated Semantics The meaning of each statement Determined by what effect it will have on the program Program Correctness o Testing, Debugging, and Revising Program Documentation o Enables programmers to understand how the program functions o Involves developing good programming style that satisfies the following principals Readability Comments should be used to document and explain the programs code
Clarity Programs should employ standard convention and should avoid programming tricks and unnecessarily obscure code Flexibility Programs should be designed and written to easily maintain and change Two Types of errors when compiling Compilation Error: syntax error o Caused by misuse of the programming language o Relatively easy to correct Log Error: semantic error o Caused by an error in the logical design of the program causing it to behave incorrectly, producing incorrect results o Cannot be detected automatically o Can only be discovered by testing o Fixing semantic error is called debugging Purpose of algorithm Coding convention Reasons for documentations Enables programmers to understand how the program functions Involves developing good programming style that satisfies the following principals o Readability Comments should be used to document and explain the programs code o Clarity
Programs should employ standard convention and should avoid programming tricks and unnecessarily obscure code o Flexibility Programs should be designed and written to easily maintain and change Literals and variables Literals fixed values which provide a value in a program Explicit values in your code that are not assigned to variables Examples 11 o "Hello There" o True o 3.14 Variable A place to temporarily store data Small containers which are given a name, and filled with data in it Conventional rules when naming a variable A variable name must begin with a letter or an underscore character, not a number or another character. The remainder of the name can contain numbers and letters A variable name cannot have punctuation marks or special characters in it Avoid any of the reserved words Variable declaration A variable declaration always contains three containers: the dim statement, the variable name, and its data type o Dim intAge as integer o Dim dblThrustRatio as Double o Dim strFirstName as String
o Dim blnTaxable as Boolean Multiple declarations on a single line are not recommended because the separation of each variable is much easier to read o Dim strName, strAddress as string Operand and operators Operators o Allow you to manipulate and evaluate operands (Variable and Value) o The Visual basic operators are grouped into the following categories: Arithmetic Assignment Comparison String Logical Types of arithmetic operator Arithmetic operators take numerical values as their operands and return a single numeric value There is only one type of arithmetic operators: binary A binary arithmetic operator requires two operands to perform its duty o + o o * o / o \ (The integer division operator performs the quotient of a division) o Mod (the modulus operator performs the remainder of a division) o ^ (exponential)
Types of assignment operator Used to assign (store) a value to a variable o =: assigns the value of the right operand to the left operand X=6 o +=: adds the left and right operands and assigns the results to the left operand X += 5 -> x = x+5 o -=: subtracts the right operand from the left operand and assigns the result to the left operand X -= 5 -> x = x-5 o *=: multiplies the two operands and assigns the result to the left operand X *= 5 -> x = x*5 o /=: Divides the left operand by the right operand and assigns the value to the left operand X /= 5 -> x/5 o \=: X \= 5 -> x = x\5 o ^=: X ^= 5 -> x = x^5 Operator precedence Expression are evaluated according to their hierarchy of precedence of the operators in the expression If an expression contains several operators at the same level, they are evaluated from left to right Operators and their precedence o Parentheses: () o Exponentiation: ^ o Multiplication & Division: * / o Integer Division: \ o Modulus: Mod o Addition & Subtraction: + -
o Equality and relational: = <> < <= > => Types of comparison operators Used to compare two variables or values and return true or false to make decisions. Comparison operators always return a Boolean result that may be used to determine the next course of execution. o <: returns true if the left operand is less than the right operand o >: returns true if the left operand is greater than the right operand o <=: returns true if the left operand is less than or equal to the right operand o >=: returns true if the left operand is greater than or equal to the right operand o =: returns true if the left operand is equal to the right operand o <>: returns true if the left operand is not equal to the right operand Examples o Operator True Example False Example < 27 < 45 45 < 27 > 98 > 97 97 > 98 <= 45 <= 45 16 <= 6 >= 98 >= 98 97 >= 98 = 98 = 98 98 = 98 <> 98 <> 97 98 <> 98 Types of logical operators Used to compare two Boolean values as operands and return a true or false result. There are three basic types of logical operators: and, or and not o Not: makes a False condition true and vise versa o And: will yield a true if and only if both expressions are true
o Or: Will yield a true if one or the other or both expressions are true If statements Allow you to make a choice among several options o One option: if o Two options: if Else o Multiple Options: If Else-If Else Comparison and logical operators are most often used to express a condition Example: o If grade >= 90 then MsgBox("A") If grade >= 80 then MsgBox ("B") If grade >= 70 then MsgBox ("C")... Else MsgBox ("F") End If Select statements
For loop Used when we know how many times we want a loop to execute A counter controlled loop o Example
This is loop number: 1 This is loop number: 2 This is loop number: 3 This is loop number: 4 for I = 1 to 4 step 1 Console.Writeline("This is loop number: &i) next While loop Uses counters, accumulators, flags and nested loops Do while o Repeats a sequence of statements either as long as or until a certain condition is true Example Dim num as integer = 1 do while num <= 7 1stNumbers.items.add(num) num += 1 Loop End Sub Do loop Until o Example Dim intnum as integer intnum = 0 do Console.Writeline("This is a loop number: "& intnum) intnum += 1 loop until (intnum <= 5) Counter Calculates the number of elements in a list
Numerical variable that keeps track of the number of items that have been processed Accumulator Sum Numerical values in list Numerical variable that totals numbers Flag Records whether certain events have occurred Subroutine Defined using a sub statement The substatement consists of a header and a body The header consists of the sub name and parameter in parentheses The naming of the sub follows the same rules as the variable Use call to call subroutine to make code more readable Exit sub Example o Sub main () dim x , y as integer x = cint (inputbox("Enter first number:")) y = cint (inputbox("Enter second number:")) Call sum (x, y) End Sub Sub Sum (byval num1 as integer, byval num2 as integer) Console.write("the is sum " & num1 + num2) End Sub Function
Defined using the function statement The function statement consist of a header and a body The header consist of the function name and parameter in the parenthesis The naming of the function follows the same rules as variables Results are returned out of a function using the statement: return expression The return statement can be used to return any valid expression that evaluates to a single value Exit function o Example Sub Main() dim x, y as integer x = cint (inputbox("Enter a number: ")) y = fsquare (x) Console.write (y) End Sub Function fsquare (byval num as integer) as integer dim I as integer I = num*num return i End function Why use procedure? Decomposition o Break problems into smaller ones Avoid repeating codes Software reusability Easier maintenance debugging and testing
What are procedures? Small modules that define specific task that may be used at many points in a program Code containers used to store a code Two types of procedures o Subroutine o Function To use subs or functions, need to know how to: o Define/declare o Pass arguments o Return the results to their calculations Subroutine Sub SubroutineName (parameter list) Statements End Sub Defined using sub statement The sub statement of a header and a body The header consist of the sub name and parameter list in parentheses The naming of sub follows the same rules as variables Use call to call subroutine to make code more readable
Sub Procedure example Sub main () Dim x, y as integer X = cint (InputBox ("Enter a number") Y=cint (InputBox ("Enter a second number") Call sum (x, y) End sub
Sub sum (ByVal num1 as integer, ByVal num2 as integer) Console.write ("The sum is "& num1 + & num2) End sub Passing You can send items to a sub procedure Passing Arguments Parameters are used to pass information into a sub or function Parameters are variables that serve as a temp storage location to hold the information that is being passed to a sub or function Both variables and literals can be passed as arguments Passing variables or literals are called a sub or function call Passing a value ByVal stands for by Value ByVal parameters retain their original value after a procedure terminates Passing a reference ByRef stands for by reference ByRef parameters can be changed by the procedure and retain the new value after the procedure terminate Function Function name (parameter list) as datatype Statements Return expression End Function Defined by using function statement
The function statement contains a header and body The header consist of the function name and parameters list in parentheses The naming of the function follows the same rules as the variable Results are returned out of a function using the statement : return expression The return statements can be used to return any valid expression that evaluates to a single value Exit function Function example Sub main () Dim x, y as integer X =cint ("InputBox ("Enter a value")) Y= fsquare (x) Console.write(y) End Sub Function fsquare (ByVal num as integer) as integer Dim I as integer I = num*num Return I End function Function vs. Procedure Both can perform similar tasks Both can call other subs and functions Use a function when you want to return one and only one value Cannot define a sub/function within the block of another function Cannot have two subs/functions with the same name
Program Examples Determines if numbers are multiples of each other Sub main () Dim num2 as integer = Val(Inputbox("Enter first number: ")) Dim num1 as integer = Val(InputBox("Enter second number: ")) Console.Write (Multiple (num1, num2) Console.Readline () End Sub If (y mod x) = 0 then Return true Else Return False Splits Number 42339 into 4 2 3 3 9 Sub min () Dim num as integer = Val (inputbox ("enter a five digit number")) Console.write (Split (num)) Console.Readline () End Sub Function split (byval num as integer) as string Dim d1, d2, d3, d4, d5 as integer D1 = num \ 10000 D2 = (num mod 10000) \1000 D3 = ((num mod 10000) mod 1000) \1000 D4 = (num \ 10) mod 10 D5 = num mod 10
Dim result as string = d1&"___", d2 & "___".....d5 Return result Computes factorial of number Sub main () Dim num as integer = Val (inputbox ("Enter a number")) Dim I as integer Dim product as integer = 1 For I = num to 1 step -1 Product = product * i Next Console.Writeline (product) Console.Readline () End sub Morse Code Sub Main() Dim str As String = (InputBox("Enter a word or single letter or digit")) Dim lettercount As Integer = str.Length Dim count As Integer Dim morsestr As String Dim strtotal As String Dim bucket As String For count = 0 To (lettercount - 1) Step 1 morsestr = str.Substring(count, 1) bucket = morsecode(morsestr) strtotal = strtotal + bucket
Next Console.WriteLine(strtotal) Console.ReadLine() End Sub Function morsecode(ByVal str As String) As String Select Case str Case "a", "A" Return ".- " Case "b", "B" Return "-... " Case "c", "C" Return "-.-. " Case "d", "D" Return "-.. " Case "e", "E" Return ". " Case "f", "F" Return "..-. " Case "g", "G" Return "--. " Case "h", "H" Return ".... " Case "i", "I" Return ".. " Case "j", "J" Return ".--- " Case "k", "K" Return "-.- " Case "l", "L" Return ".-.. " Case "m", "M"
Return "-- " Case "n", "N" Return "-. " Case "o", "O" Return "--- " Case "p", "P" Return ".--. " Case "q", "Q" Return "--.- " Case "r", "R" Return ".-. " Case "s", "S" Return "... " Case "t", "T" Return "- " Case "u", "U" Return "..- " Case "v", "V" Return "...- " Case "w", "W" Return ".-- " Case "x", "X" Return "-..- " Case "y", "Y" Return "-.-- " Case "z", "Z" Return "--.. " Case "0" Return "----- " Case "1" Return ".---- " Case "2" Return "..--- " Case "3" Return "...-- "
Case "4" Return "....- " Case "5" Return "..... " Case "6" Return "-.... " Case "7" Return "--... " Case "8" Return "---.. " Case "9" Return "----. " Case " " Return " " End Select
End Function End Module Find Average of 5 numbers Sub Main() Dim NUMBER As Integer Dim AVERAGE As Integer Dim COUNT As Integer Dim SUM As Integer Dim INDEX As Integer Console.Write("Please type a value for NumValue: ") COUNT = Console.ReadLine() SUM = 0 For INDEX = 1 To COUNT Console.Write("Please type a value for Num: ") NUMBER = Console.ReadLine() SUM = SUM + NUMBER
Next INDEX AVERAGE = SUM / COUNT Console.WriteLine("The Average is " & AVERAGE) Console.ReadLine() End Sub Displays largest number entered Sub Main() Dim NUMBER As Integer Dim LARGEST As Integer Dim NUM As Integer Console.Write("Please type a value for Num: ") NUMBER = Console.ReadLine() LARGEST = 0 Do While (NUM <> -1) If (NUM > LARGEST) Then LARGEST = NUM End If Console.Write("Please type a value for Num: ") NUM = Console.ReadLine() Loop Console.WriteLine("The Largest value entered was " & LARGEST) Console.ReadLine() End Sub