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AITT4300_Chapter1.pdf
Chapter 1 An Introduction to Programming AITT 4300 DIGITAL COMPUTER STRUCTURES
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
1.1 What is Programming?
A program is a list of instructions that is executed by a computer to accomplish a particular task. Creating those instructions is programming. Program development cycle: ◦ Analyze the problem ◦ Design a program to solve the problem ◦ Code the program ◦ Test the program ◦ Revise as necessary
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
1.2 Basic Programming Concepts Important concepts: ◦ Pseudocode is used to plan out the logic of a computer program, using English words and phrases.
◦ Input refers to information that is accepted into the program from the user or other sources.
◦ Variables represent values within a program. ◦ Constants are values used within a program. The value of a constant does not change (i.e., it is constant) throughout the program.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Example: The Music Purchase Program
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Compute the cost of downloading music online. Pseudocode used: ◦ Input the number of songs to purchase, Songs
Input Songs ◦ Compute the total cost:
Set DollarPrice = 0.99 * Songs ◦ Output the total cost:
Write DollarPrice ◦ Variables used: Songs and DollarPrice ◦ Constants: 0.99
Java Code for the Music Purchase Program
1. public static void main (String[] args) 2. { 3. int Songs = 0; 4. float DollarPrice = 0.0; 5. Scanner scanner = New Scanner(system.in) 6. println(“Enter the number of songs you wish to
purchase today.”); 7. Songs = scanner.nextInt(); 8. DollarPrice = 0.99 * Songs; 9. println(DollarPrice); 10.}
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
C++ Code for the Music Purchase Program 1. void main(void)
2. {
3. int Songs;
4. float DollarPrice;
5. cout << “Enter the number of songs you wish
to purchase today.”;
6. cin >> Songs;
7. DollarPrice = 0.99 * Songs;
8. cout << DollarPrice;
9. return;
10. }
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Data Input Input operations get data into the programs
A user is prompted for the data to be entered ◦ This text uses the word Write to indicate a prompt for input ◦ The word Input indicates that a user has entered a value ◦ Example:
Write “Enter the number of songs you wish to purchase today.”
Input Songs ◦ Other types of input can be from a file, dragged by mouse, and more
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Variables and Constants Data is input into a program variable. A variable is a named piece of memory whose value can change during the running of the program. Example:
Write “Enter the number of songs you wish to purchase today.”
Input Songs
The variable is Songs. A value which cannot change as the program runs is a constant. In this example, the constant is 0.99.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Input Prompts
A prompt indicates to the user that data should be input. To get the user to enter one number: Write “Enter a number: ” prompts the user to enter a number Input Number stores the number in the variable, Number
To get the user to enter two numbers: Write “Enter two numbers: ” prompts the user to enter 2 numbers Input Number1 stores the numbers in 2 variables, Input Number2 Number1 and Number2 The prompt is the Write statement
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Naming Variables All variable names must be one word
Spaces are never allowed
Variables cannot begin with a number
Names should be meaningful
Long names are allowed but names should be as short as possible, yet still be meaningful
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Variable Name Examples Some examples:
Miles_traveled is fine Miles Traveled is not (space) TaxRate_1 is fine 1_TaxRate is not (begins with a number) Variable1 is fine but not meaningful Z is fine but not meaningful
What’s wrong with these? My Number 2_4_6_8_go CowWhoJumpedOverTheMoon #
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
What’s really happening?
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
A variable is the name for a storage location in the computer’s internal memory.
The value of a variable is the contents of that location. The contents of the computer’s memory after the Input statement in the Music Purchase program is executed and the user wants to download 78 songs:
The DollarPricemailbox is empty – it has not yet been assigned a value. At the end of the program, the contents of memory would be:
Every time you run the program with a different number of songs, the values in the memory locations will change. The contents of the Songsmemory “box” will be replaced by the new number of songs and, after the calculation is made, the contents of the DollarPricememory location will be replaced by the new value.
Try It Suppose a program is to calculate the final (maturity) value of an investment. You will be given the amount invested, the rate of interest, and the length of time that the money is invested.
a. What data must be input to this program?
b. Give reasonable names for each of the input variables.
c. Give Write and Input statements that prompt for and input the data for this problem.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
1.3 Data Processing and Output Set DollarPrice = 0.99 * Songs
The above statement is a processing statement. ◦ It means to take the value in the variable Songs, multiply it by 0.99, and set the value of the variable DollarPrice to the result of the multiplication.
It is also an assignment statement. ◦ It changes the value of the variable DollarPrice from its previous value to the new value.
Write DollarPrice This output statement will output the value of DollarPrice to the screen.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Assigning and Reassigning Values to Variables
In a program the following two statements: Set NumberX = 45 Set NumberX = 97
will first assign the value of 45 to the variable, NumberX and then replace that value with 97. After these two statements are executed, NumberX contains the value of 97. The value 45 has been lost.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Operations on Data: Arithmetic Operations
+ Addition 2 + 3 = 5 - Subtraction 7 – 3 = 4 * Multiplication 5 * 4 = 20 / Division 12/3 = 4 ^ Exponentiation 2^3 = 8 % Modulus 14 % 3 = 2
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
The Modulus Operator The modulus operator returns the remainder after dividing one number by another.
15 % 2 = 1 because 15 ÷ 2 = 7 with a remainder of 1 39 % 4 = 3 because 39 ÷ 4 = 9 with a remainder of 3 21 % 7 = 0 because 21 ÷ 7 = 3 with a remainder of 0
The modulus operator has many uses which are not immediately obvious. For example, to test if a number is odd or even, if X is any integer:
If X % 2 = 1, the number is odd If X % 2 = 0, the number is even
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Hierarchy of Operations o First: perform operations inside parentheses (from inside out if more than one)
o Second: perform exponentiation
o Third: do multiplications, divisions, and modulus from left to right (if there are more than one)
o Fourth: do additions and subtractions from left to right (if there are more than one)
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Example of Hierarchy of Operations 3*(6+2)/12+(7– 5)^2*3 = ?
( ) first: = 3*8/12+2^2*3
^ next: = 3*8/12+4*3
Leftmost * next:= 24/12+4*3
Division next: = 2+4*3
Multiply next: = 2+12
Addition last: = 14
3*6+2/12+(7–5)^(2*3) = ?
( ) first: = 3*6+2/12+2^6
^ next: = 3*6+2/12+64
Leftmost * next: = 18+2/12+64
Division next: = 18+.167+64
Leftmost + next:= 18.167+64
Final + last: = 82.167
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Data Output
Data that is sent from the program to the screen, printer, or to a file is output. In pseudocode, the following statement will display the value of the variable to the screen and send the cursor to the next line:
Write DollarPrice
If DollarPrice contains the value 9.90, the output on the screen will be:
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
9.90
Annotate the Output If the output consists of numbers or any data that has no explanatory text with it, you should annotate your output
Annotating output means to add some text so the user knows what the output means.
Example: if Test1 and Test2 are 2 exam scores for a student: Average = (Test1 + Test2)/2 Write “The student’s average is: “ Write Average
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Formatting Output
In a program the following two statements: Write “The cost of your purchase is “
Write DollarPrice
will produce the following output: The cost of your purchase is
9.90
However, the following single statement:
Write “The cost of your purchase is ” + DollarPrice + “ dollars.”
will produce the following output:
The cost of your purchase is 9.90 dollars.
Note that the text inside the “ ” is output to the user as is, and it is the value of the variable that is output.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Formatting Output Be careful to format your output so there are appropriate spaces.
If Number1 is a variable with the value of 8, Number2 is a variable with the value of 6, and Sum is a variable that holds the value of Number1 + Number2:
The statement: Write “The sum of” + Number1 + “and” + Number2 + “is” + Sum
will produce the following output: The sum of8and6is14
However, the statement: Write “The sum of ” + Number1 + “ and ” + Number2 + “ is ” + Sum
will produce the following output: The sum of 8 and 6 is 14
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
1.4 Data Types Each piece of data (a single character, a number, a paragraph, etc.) is stored in at least one memory location. The amount of space allocated to data initially depends on the data type.
Some languages have many data types, such as integer, floating point data, strings, characters, Boolean types, double, and so on.
Some languages have only a few data types such as numeric and string.
Some languages insist that a data type is declared before it is used and the type can never change. These are called strictly typed languages.
Other languages are not as strict about declaring data types and are called loosely typed.
We will declare our data types in our pseudocode.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
The Declare Statement Variables should be declared to identify their data type. In this text, a statement such as the following will set aside a space in the computer’s memory to store a variable of a given data type:
Declare VariableName As DataType
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Character and String Data Character data (alphanumerics) ◦ Consists of all the characters you can type at the keyboard ◦ A character string (i.e., a string) is a sequence of characters. ◦ The data type is String or Character ◦ If a variable is of String or Character type, you cannot perform any math operations on it.
◦ However, you can join two Characters or Strings
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Declaring Character and String Variables
The following statement declares a variable named Response to be of Character data type:
Declare Response As Character A Character variable can contain only a single character. The following statement declares a variable named UserName to be of String data type:
Declare UserName As String A String variable can contain as many characters as desired but the whole string of characters must be enclosed within the quotes. ◦ Note that spaces, punctuation, and special symbols such as the %, @, *, and so forth are all considered characters.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Concatenation If a variable is of String or Character type, you cannot perform any math operations on it. However, you can join (concatenate) two Characters or Strings: ◦ Given: First, Last, and Full are three String variables ◦ Given: First = “Lizzy” and Last = “Duck” ◦ Then the statement
Set Full = First + “ “ + Last
will assign the value “Lizzy Duck” to Full Note: The space enclosed in quotes is necessary to put a space between the first and last name when stored in the variable Full.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Integer Data Integers are all the positive, negative, or zero whole numbers
Examples: 8 is an integer 8.3 is not an integer -24,567,890 is an integer 0 is an integer 4.0 is not an integer because it has a decimal part
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Declaring Integer Variables Each language has a specific way to declare the data type of its variables.
o In this text we use: Declare VariableName As Integer
o In C++ and Java: int VariableName;
o In Visual Basic: Dim VariableName As Integer
o In JavaScript a variable is given a type when it gets its initial value. Therefore: var VariableName = 0;
sets the JavaScript variable to be an integer
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Floating Point Variables All floating point numbers have both an integer part and a fractional part
Examples: 5.65 9.00 -456,784.983 ½ Repeating numbers like 0.333333… Irrational numbers like pi (π) or sqrt(2) Note: 7 is not a floating point number but 7.0 is!
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
The Declare Statement Revisited In this text we will declare variables with the following data types: ◦ To declare a variable named Number1 as a floating point variable use:
Declare Number1 As Float
◦ To declare a variable named Number2 as an integer variable use:
Declare Number2 As Integer
◦ To declare a variable named OneLetter as a character variable use:
Declare OneLetter As Character
◦ To declare a variable named OneWord as a string variable use:
Declare OneWord As String
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Naming Conventions Some programmers use specific conventions when naming variables. These are almost always simply a matter of preference.
CamelBack notation examples: Visual Basic convention examples: Declare NumberOne As Integer Dim intNumberOne As Integer
Declare firstName As String Dim strFirstName As String
Declare Tax_rate As Float Dim lngTaxRate As Long (Float)
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
Boolean Data
• Named for George Boole who developed the algebra of logic, basic to the design of digital computer circuits. • A variable of Boolean data type can have only one of two values: true or false. • A 1 represents true and a 0 represents false. • We use the following pseudocode to declare a Boolean variable:
Declare Status As Boolean • The uses for Boolean variables will become evident as you continue to write programs.
PRELUDE TO PROGRAMMING, 6TH EDITION BY ELIZABETH DRAKE
