chapter 4: variables, constants, and arithmetic operators introduction to programming with c++...
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Chapter 4: Variables, Constants, and
Arithmetic Operators
Introduction to Programming with C++Fourth Edition
Introduction to Programming with C++, Fourth Edition 2
Objectives
• Distinguish among a variable, a named constant, and a literal constant
• Select an appropriate name, data type, and initial value for a memory location
• Explain how data is stored in memory• Declare and initialize a memory location• Type cast data
Introduction to Programming with C++, Fourth Edition 3
Objectives (continued)
• Use an assignment statement to assign data to a variable
• Include arithmetic operators in an expression• Get string input using the getline() function• Ignore characters using the ignore() function
Introduction to Programming with C++, Fourth Edition 4
Variables and Named Constants
• Variable – the only type of memory location whose contents can change while a program is running
• Named Constant – used for any item whose value will remain the same each time the program is executed
Introduction to Programming with C++, Fourth Edition 5
Circle Area Problem
Introduction to Programming with C++, Fourth Edition 6
Selecting a Name for a Memory Location
• Identifier – a descriptive name assigned to each variable and named constant used in a program
• Keyword (reserved word) - a word that has a special meaning in a programming language
Introduction to Programming with C++, Fourth Edition 7
Naming Rules
Introduction to Programming with C++, Fourth Edition 8
Valid Names and Keywords
Introduction to Programming with C++, Fourth Edition 9
Selecting a Data Type for a Memory Location
• Data types - control the type of data the memory location can store
• Fundamental data types - basic data types built into the C++ language which must be typed using lowercase letters
• Integers - whole numbers
Introduction to Programming with C++, Fourth Edition 10
Selecting a Data Type for a Memory Location (continued)
• Floating-point numbers - numbers with a decimal place
• Characters - letters, symbols, and numbers that will not be used in calculations
• Boolean values - true or false
Introduction to Programming with C++, Fourth Edition 11
Names of Memory Locations for the Circle Area Problem
Introduction to Programming with C++, Fourth Edition 12
Some of the Data Types Available in C++
Introduction to Programming with C++, Fourth Edition 13
Data Type Assigned to the Memory Locations for the Circle Area
Problem
Introduction to Programming with C++, Fourth Edition 14
How Data is Stored in Internal Memory
• Numeric data – represented in internal memory using the binary (or base 2) number system
• Character data - represented in internal memory using ASCII codes
Introduction to Programming with C++, Fourth Edition 15
Comparison of the Decimal and Binary Number Systems
Introduction to Programming with C++, Fourth Edition 16
Partial ASCII Chart
Introduction to Programming with C++, Fourth Edition 17
Selecting an Initial Value for a Memory Location
• Initializing - assigning an initial, or beginning, value to a memory location
• Literal constant - an item of data that can appear in a program instruction, and can be stored in a memory location
• Numeric literal constant - a number
Introduction to Programming with C++, Fourth Edition 18
Selecting an Initial Value for a Memory Location (continued)
• Character literal constant - a character enclosed in single quotation marks
• String literal constant - zero or more characters enclosed in double quotation marks
Introduction to Programming with C++, Fourth Edition 19
Examples of Numeric, Character, and String Literal Constants
Introduction to Programming with C++, Fourth Edition 20
Type Casting
• Implicit type conversion – in an assignment, if the data type of the expression does not match that of the memory location, the data is converted appropriately– Converts values to fit memory locations
• Conversion can either promote values to a larger type or demote values to a smaller type (loss of data)
Introduction to Programming with C++, Fourth Edition 21
Type Casting (continued)
Introduction to Programming with C++, Fourth Edition 22
Type Casting (continued)
• Type casting (explicit type conversion) – the forced conversion of data from one data type to another
• Enclose an item of data in parentheses, preceded by the desired type
• Example - type cast the double number 3.7 to the float data type by writing float(3.7)
Introduction to Programming with C++, Fourth Edition 23
Initial Values Assigned to Memory Locations for the Circle Area
Problem
Introduction to Programming with C++, Fourth Edition 24
Declaring a Named Constant
• To declare a named constant specify:– Name– Data type– Initial value
• Can use the named constant anywhere the initial value can be used– Even in other named constants
Introduction to Programming with C++, Fourth Edition 25
Declaring a Named Constant (continued)
Introduction to Programming with C++, Fourth Edition 26
Declaring a Variable
• To declare a variable specify:– Name– Data type– Initial value (optional)
• If you omit the initial value, the variable may contain garbage (left over bits)
Introduction to Programming with C++, Fourth Edition 27
Syntax and Examples of Instructions that Reserve and Initialize Variables
in C++
Introduction to Programming with C++, Fourth Edition 28
C++ Statements Reserving the radius, radiusSquared, and area
Variables
Introduction to Programming with C++, Fourth Edition 29
Using an Assignment Statement to Store Data in a Variable
• Use an assignment statement to change the contents of a variable while a program is running
• Assigns the value of the expression appearing on the right side of the assignment operator (=) to the variable whose variablename appears on the left side
• Remember that a variable can store only one value at a time: new assignments replace old
Introduction to Programming with C++, Fourth Edition 30
Using an Assignment Statement to Store Data in a Variable (continued)
Introduction to Programming with C++, Fourth Edition 31
Processing of Assignment Statements
int temp = 3;temp = temp + 1;temp = temp * 2;
• Declaration statement int temp = 3: creates a temp variable in the computer’s internal memory and initializes the variable to the integer 3
• The assignment statement temp = temp + 1: adds the number 1 to the contents of the temp variable, giving 4. It then replaces the 3 currently stored in the temp variable with the number 4
Introduction to Programming with C++, Fourth Edition 32
Processing of Assignment Statements (continued)
• The assignment statement temp = temp * 2: first multiplies the contents of the temp variable (4) by 2, giving 8. It then removes the number 4 from the temp variable and stores the number 8 there instead
Introduction to Programming with C++, Fourth Edition 33
Arithmetic Operators
Introduction to Programming with C++, Fourth Edition 34
Arithmetic Operators (continued)
Introduction to Programming with C++, Fourth Edition 35
Getting Data from the Keyboard
• Use cin and the extraction operator (>>) to input data from the keyboard
• Can input a single character or a string, as long as the string has no spaces
• The getline() function gets string input from the keyboard (including embedded spaces)
Introduction to Programming with C++, Fourth Edition 36
Getting Data from the Keyboard (continued)
Introduction to Programming with C++, Fourth Edition 37
The ignore() Function
• Instructs the computer to disregard, or skip, characters entered at the keyboard
• The function reads and discards (consumes) the characters
• Necessary when inputting numbers and characters
Introduction to Programming with C++, Fourth Edition 38
The ignore() Function (continued)
Introduction to Programming with C++, Fourth Edition 39
Summary
• Variables and constants need:– Name, data type, initial value
• Type casting converts values to fit memory locations
• Assignments change the contents of a variable while a program is running
• Use arithmetic operators in expressions• Use getline() to input strings with spaces• Use ignore() to consume unwanted characters
from input stream
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