Chapter 4: Variables, Constants, and

Arithmetic Operators

Introduction to Programming with C++Fourth Edition

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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

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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

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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

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Circle Area Problem

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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

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Naming Rules

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Valid Names and Keywords

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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

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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

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Names of Memory Locations for the Circle Area Problem

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Some of the Data Types Available in C++

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Data Type Assigned to the Memory Locations for the Circle Area

Problem

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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

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Comparison of the Decimal and Binary Number Systems

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Partial ASCII Chart

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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

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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

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Examples of Numeric, Character, and String Literal Constants

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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)

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Type Casting (continued)

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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)

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Initial Values Assigned to Memory Locations for the Circle Area

Problem

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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

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Declaring a Named Constant (continued)

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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)

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Syntax and Examples of Instructions that Reserve and Initialize Variables

in C++

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C++ Statements Reserving the radius, radiusSquared, and area

Variables

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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

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Using an Assignment Statement to Store Data in a Variable (continued)

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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

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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

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Arithmetic Operators

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Arithmetic Operators (continued)

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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)

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Getting Data from the Keyboard (continued)

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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

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The ignore() Function (continued)

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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