Transcript TA1: An Introduction to Programming

Chapter 1:
Introduction to Programming
Extended Prelude to Programming
Concepts & Design, 3/e
by
Stewart Venit and Elizabeth Drake
Copyright © 2007 Pearson Education, Inc. Publishing as Pearson Addison-Wesley
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
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1.2 Basic Programming Concepts
• A simple programming problem: convert a
price from British pounds into U.S. dollars.
• Pseudocode
• Input the price of the item, PoundPrice, in pounds
• Compute the price of the item in dollars:
Set DollarPrice = 1.62 * PoundPrice
Write DollarPrice
– Variables used: PoundPrice and DollarPrice
– Constants: 1.62
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BASIC and C++ Code
BASIC Code:
DIM PoundPrice As Double
DIM DollarPrice As Double
INPUT PoundPrice
LET DollarPrice = 1.62 * PoundPrice
PRINT DollarPrice
END
C++ Code:
void main(void)
{
float PoundPrice, Dollar Price;
cout << “Enter price in Pounds.”;
cin >> PoundPrice;
DollarPrice = 1.62 * PoundPrice;
cout << DollarPrice;
}
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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 price in pounds”
Input PoundPrice
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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 price in pounds”
Input PoundPrice
• The variable is PoundPrice.
• A value which cannot change is a constant. In this
example, the constant is 1.62
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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
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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
What’s wrong with these?
• My Number
• 2_4_6_8_go
• CowWhoJumpedOverTheMoon
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1.3 Data Processing and Output
 Set DollarPrice = 1.62 * PoundPrice
The above statement is a processing statement. Take the value in
the variable PoundPrice, multiply it by 1.62, and set the
value of the variable DollarPrice to the result of the
multiplication.
 Write DollarPrice
Output the value in DollarPrice to the monitor.
Assignment statements change the value in a variable
 Set counter = counter + 1
Take the value of counter, add 1, and store the result
back in the same variable.
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Arithmetic Operations
+
*
/
^
%
Addition
Subtraction
Multiplication
Division
Exponentiation
Modulus
2+3
7–3
5*4
12 / 3
2^3
14 % 3
=
=
=
=
=
=
5
4
20
4
8
2
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Hierarchy of Operations
1st: perform operations inside parentheses (from
inside out if more than one)
2nd: perform exponentiation
3rd: do multiplications, divisions, and modulus
from left to right (if there are more than one)
4th: do additions and subtractions from left to
right (if there are more than one)
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Example of Hierarchy of Operations
3 * (6 + 2) / 12 – (7 – 5) ^ 2 * 3 = ?
( ) first:
^ next:
Leftmost * next:
Division next:
Multiply next:
Subtract last:
= 3 * 8 / 12 – 2 ^ 2 * 3
= 3 * 8 / 12 – 4 * 3
= 24 / 12 – 4 * 3
=2–4*3
= 2 – 12
= -10
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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
• Given the following statement:
Write “The price of the item is”,
DollarPrice, “ dollars”
• The output will look like this:
The price of the item is 162 dollars
• Note that the text inside the “ ” is output to the user as is, and
it is the value in the variable that is output.
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Annotate the Output
• If the output consists of numbers or any data that has
no explanatory text with it, you should annotate your
output – this 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: “  annotated
Write Average
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1.4 Types of Data
• Numeric Data
– Integer data (whole numbers)
• 10 25 -45
0
– Real (Floating point) data (numbers that have a decimal
point)
• 23.5
-5.0
– Note: 5 and 5.0 are stored differently in a computer even
though they have the same value. The first, 5 is an Integer
but the second, 5.0 is a Real number.
• Character data (alphanumerics)
– All the characters you can type at the keyboard
– The type is String or Character
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The Declare Statement
• Variables should be declared to identify what
the type is.
• We use the following:
– Declare MyWholeNumber As Integer
– Declare MyDecimalNumber As Real
– Declare MyText As String
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Exponential Notation
• Scientific notation:
680,000 = 6.8 x 105
1,502,000,000 = 1.502 x 109
0.068 = 6.8 x 10-2
0.00001502 = 1.502 x 10-5
• Exponential notation:
680,000 = 6.8E+5
1,502,000,000 = 1.502E+9
0.068 = 6.8E-2
0.00001502 = 1.502E-5
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Character String Data
• Character: any symbol that can be typed at the
keyboard
• Character string: a sequence of characters
• Character and String Data Types:
– Declare MyInitial As Character
declares a variable named MyInitial as a
Character type
– Declare MyName As String declares a
variable named MyName as a String type
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Concatenation
• Concatenation takes two strings and joins them to
create a string result
• The concatenation operator is symbolized, in
pseudocode, with a + sign
• Example: if:
String1 = “yellow” and String2 = “duckie”
then the statement:
Set MyFriend = String1 + String2
results in:
MyFriend = “yellow duckie”
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Pseudocode Language (Ch 1)
Our pseudocode language will be expanded throughout the text. In this chapter
we learned how to input, output, assign values to variables, and perform
arithmetic calculations.
Input
Input Variable
Assignment
Set Variable = 10
Set Variable = AnotherVariable
Output
Arithmetic Operations
Write “literal text”
Write Variable
() ^ * / % + Write “literal text”, Variable
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