egr 2261 unit 2 basic elements of c++ read malik, chapter 2. homework #2 and lab #2 due next week....

EGR 2261 Unit 2Basic Elements of C++

Read Malik, Chapter 2. Homework #2 and Lab #2 due next

week. Quiz next week.

A Quick Look at a C++ Program

C++ Programming: From Problem Analysis to Program Design, Seventh Edition 2

A Quick Look at a C++ Program (cont’d.)

• Sample run:

3C++ Programming: From Problem Analysis to Program Design, Seventh Edition

A Quick Look at a C++ Program(cont’d.)



• Variable: a memory location whose contents can be changed.


Figure 2-2 Memory allocation after the four variable declaration statements

Figure 2-3 Memory spaces after the statement length = 6.0; executes

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The Basics of a C++ Program

• Function (or subprogram): a collection of statements that, when executed, accomplishes something useful.– May be predefined or user-defined.

• Syntax rules: rules that specify which statements (instructions) are legal or valid.

• Semantic rules: determine the meaning of the instructions.

• Programming language: a set of rules, special symbols, and reserved words.


Special Symbols

• Some special symbols in C++ :

• This is not a complete list of special symbols.


Reserved Words (Keywords)

• Reserved words (or keywords):– You cannot redefine these words.– You cannot use them for anything other than their

intended use.Examples:

– int– using– return

– See Appendix A (next slide) in textbook for complete list.


Tokens

• Tokens: the smallest meaningful units of a program.• C++ tokens include special symbols, reserved words,

and identifiers.


Reserved words Identifier Special symbol

Identifiers

• Identifier: the name of something that appears in a program.– Consists of letters, digits, and the underscore character (_).– Must begin with a letter or underscore.

• C++ is case sensitive.– NUMBER is not the same as number.

• Two predefined identifiers are cout and cin.• Unlike reserved words, predefined identifiers may be

redefined, but it is not a good idea.


Identifiers (cont’d.)

• Examples of legal identifiers in C++:• first• payRate2• Employee_Salary


Comments

• Comments are for the reader, not the compiler.• Two types:

– Single line: begin with //// This is a C++ program. // Welcome to C++ Programming.

– Multiple line: enclosed between /* and *//* You can include comments that can occupy several lines.*/


Whitespace

• Every C++ program contains whitespace.– Includes blanks, tabs, and newline characters.

• Whitespace must separate reserved words and identifiers from each other.

• Proper use of whitespace (such as indenting) can also make programs more readable.


Data Types

• Data type: set of values together with a set of allowed operations on those values.

• C++ data types fall into three categories:– Simple data types– Structured data types– Pointers

• For the next few weeks we’ll mostly use simple data types.


Simple Data Types

• Three categories of simple data:– Integral: integers (numbers without a decimal).

• Can be further categorized:– char, short, int, long, long long, bool, unsigned char, unsigned short, unsigned int, unsigned long

– Floating-point: decimal numbers.• Can be further categorized:

– float, double, long double– Enumeration type: user-defined data type. We won’t use.


Partial Hierarchy of Data Types

Data Types

Simple Data Types

Integral(int, bool,

char, …)

Floating-Point

(float, double,

…)

Enumeration

Structured Data Types Pointers

Simple Data Types (cont’d.)

• The ranges shown above are typical. Different compilers may allow different ranges of values.


int Data Type

• Examples of int data:-6728078+763

• Do not use commas within numbers. Typing 1,430 instead of 1430 will usually cause an error.


bool Data Type

• The bool type has only two possible values: true and false.– For keeping track of true/false (Boolean)

information, such as whether a person’s age is greater than 21.

• This is considered an integral data type because it’s actually implemented as a 0 for false and a 1 for true.


char Data Type

• Used for single characters: letters, digits, and special symbols.

• Each character is enclosed in single quotes:– 'A', 'a', '0', '*', '+', '$', '&'

• A blank space is a character.– Written ' ', with a space left between the single quotes.


char Data Type (cont’d.)

• Different character sets exist, but we’ll use ASCII.• ASCII: American Standard Code for Information

Interchange– Each of 128 integer values (from 0 to 127) represents a

different character; see Appendix C in textbook (next slide).

– Collating sequence: Characters have a predefined ordering based on the ASCII numeric value.For example, the ASCII code for 'A' is 65 and the ASCII code for ‘D' is 68, so we can say that 'A' < ‘D'.


Floating-Point Data Types

• Non-integer numbers can be entered or displayed using decimal notation or using a modified scientific notation.


Floating-Point Data Types (cont’d.)

• float– Typical Range: -3.4E+38 to 3.4E+38 (four bytes)

• double– Typical Range: -1.7E+308 to 1.7E+308 (eight bytes)

• Ranges of data types are system-dependent.• We’ll generally use double when we want a

floating-point number.


Review: Simple Data Types

• Three categories of simple data:– Integral: integers (numbers without a decimal)

• Can be further categorized:– char, short, int, long, long long, bool, unsigned char, unsigned short, unsigned int, unsigned long

– Floating-point: decimal numbers• Can be further categorized:

– float, double, long double– Enumeration type: user-defined data type. We won’t use.


Arithmetic Operators

• Some C++ arithmetic operators:• + addition• - subtraction• * multiplication• / division• % modulus (or remainder)

• You can use +, -, *, and / with integral and floating-point data types.

• You can use % only with integral data types.


Arithmetic Expressions

• Arithmetic expressions combine values (operands) and arithmetic operators to yield a result.

• Example: 12.8 * 17.5 - 34.50

• Arithmetic expressions can be:– Integral expressions: all operands are integers.– Floating-point expressions: all operands are floating-point.– Mixed expressions: some operands are integer, some are

floating-point.


Integral Expressions

• Integral expression: an arithmetic expression in which all operands are integers.– Yields an integer result.– Example: 2 + 3 * 5

– Caution: When you use / with integers, the integer result is truncated (no rounding).

– Example: 7 / 2 yields a result of 3


• We know that 7 ÷ 2 = 3.5

• Recall that another way to say this is that 7 ÷ 2 = 3 with a remainder of 1.

• In this example, 3 is called the quotient and 1 is called the remainder.

• In C++, using the / operator with integers yields the quotient.

• Example: In C++, 7 / 2 yields a result of 3

• And using the % operator with integers yields the remainder.

• Example: In C++, 7 % 2 yields a result of 1

Quotient and Remainder

Floating-Point Expressions

• Floating-point expression: an arithmetic expression in which all operands are floating-point.– Yields a floating-point result.– Example: 7.0 / 2.0

• The expression above yields 3.5

– Another example: 12.8 * 17.5 - 34.50


Operator Precedence and Associativity

• Operators inside parentheses are evaluated first.• *, /, and % have the same level of precedence and

are evaluated next.• + and – have the same level of precedence and are

evaluated next.• Arithmetic operators on the same level of

precedence are performed from left to right. (They have “left-to-right associativity.”)

• Example: Evaluate the following expression: 3 * 7 - 6 + 2 * 5 / 4 + 6


Mixed Expressions

• Mixed expression: an arithmetic expression that has operands of different data types (some integer, some floating-point).

• Examples:2 + 3.56 / 4 + 3.95.4 * 2 - (3.6 + 5) / 2

• See next slide for rules on how C++ evaluates these.


Mixed Expressions (cont’d.)

• Evaluation rules:– The precedence and associativity rules from above

still apply.– If an operator has the same types of operands:

• It is evaluated according to the type of the operands.

– If operator has both types of operands:• Integer is “promoted” to floating-point.• Operator is evaluated.• Result is floating-point.


Type Conversion and Casting

• Implicit type conversion (also called coercion) occurs when C++ automatically changes a value of one type to another type. We’ve seen an example of this with mixed expressions.

• C++ also lets you perform explicit type conversion using the cast operator:static_cast<dataTypeName>(expression)


Type Conversion (Casting) (cont’d.)


Unary Versus Binary Operators

• The arithmetic operators we’ve discussed are all binary operators: they take two operands.

• Some operators are unary operators (one operand). • In fact, + and – can be either binary or unary,

depending on the context.• Unary – is negation.• Example: –2 * 3• Another example: +2 * –3


Other Operators

• As well as the arithmetic operators discussed above, C++ has many other operators.

• See Appendix B (next slide) in the textbook for a complete list that shows precedence and associativity. – Note from this list that unary + and – have higher

precedence than binary + and – .

• Unfortunately the table in Appendix B contains a few typos, so be sure to fix them using the list of textbook typos on the course website.


http://people.sinclair.edu/nickreeder/egr2261/malikErrata.htm

Review: Data Types

• Recall that C++ data types fall into three categories:– Simple data types (int, char, bool, double, …)

– Structured data types– Pointers

• For the next few weeks we’ll mostly use simple data types, plus one structured data type called the string type.


string Type

• A string is a sequence of zero or more characters enclosed in double quotation marks.– Contrast with char data type, which is a single character

inside single quotation marks.

• A string’s length is the number of characters in it.– Example: length of "William Jacob" is 13

• Each character has a position in the string, with the first character at position 0.– Example: In "William Jacob", the character ‘m’ is at

position 6.


string Type (cont’d.)

• Unlike the simple data types discussed earlier, string is not built into the core C++ language. It’s a programmer-defined type supplied in the C++ Standard Library.

• So the five data types that we will use extensively are– int– char– bool– double– string


Variables

• The expressions we’ve looked at used constant numeric values.– Example: 2 * 3.5

• In most programs you’ll also use variables, which are named memory locations whose values can change as the program runs.– Example: 2 * payRate

• When naming your variables, be sure to follow the rules we saw earlier for identifiers.


• In C++ you must declare each variable’s data type before you can use the variable.

• Syntax to declare one or more variables:

Declaring Variables


Putting Data into Variables

• A variable is said to be initialized the first time you place a value into it.

• A variable that has not been initialized will hold an unpredictable “garbage” value. Visual Studio gives an error message if you use an uninitialized variable in an expression.

• Ways to place data into a variable:– Use an assignment statement.– Use input (read) statements.


Assignment Statement

• The assignment statement takes the form:

• The expression is evaluated and its value is assigned to the variable on the left side.

• Examples:dailyRate = 0.0002;

annualRate = 365 * dailyRate;

• In C++, = is called the assignment operator.


Assignment Statement (cont’d.)


Declaring & Initializing Variables

• You can use the assignment operator to initialize a variable in the same statement that declares it.

• Examples:int first = 13, second = 10;char ch = ' ';double x = 12.6;


Assignment versus Equality

• The = operator in C++ has a different meaning from the meaning it has in your math classes.

• Example: in a math class, the following statement cannot be true:

x = x + 1;• But this is a perfectly good (and

frequently used) C++ statement. It tells the program to increase x’s value by 1.

Increment and Decrement Operators

• The increment operator ++ increases a variable by 1.– Example: The statement

x++;does the same thing as the statement x = x + 1;

• Similarly, the decrement operator -- decreases a variable’s value by 1.– Example: The statement

x--;does the same thing as the statement x = x - 1;


Pre- and Post-Increment/Decrement

• These operators’ behavior depends on whether they’re placed before or after the variable name.– Pre-increment: ++variable increments the variable, and then uses

the incremented value in the expression.– Post-increment: variable++ uses the variable’s original value in

the expression, and then increments the variable.

• What is the difference between the following?

• Similarly for pre-decrement (--variable) and post-decrement (variable--).

C++ Programming: From Problem Analysis to Program Design, Seventh Edition

x = 5;y = ++x;

x = 5;y = x++;

52

Input (Read) Statement

• cin is used with >> to let the user enter a value.

• This is called an input statement (or read statement).• The operator >> is the stream extraction operator.• For example, if miles is a double variable, the following

statement causes computer to get a value of type double from the keyboard and place it in the variable miles:

cin >> miles;


Input (Read) Statement (cont’d.)

• A single input statement can assign values to more than one variable.

• Example: if feet and inches are variables of type int, the following statement reads two integers from the keyboard and places these integer values in feet and inches respectively. : cin >> feet >> inches;


Output Statement

• cout is used with << to display values on the screen:

• This is called an output statement.• The operator << is the stream insertion operator.• The expression is evaluated and its value is printed at

the current cursor position on the screen.


Manipulators in Output Statements

• You can use manipulators to format the output.– Example: the manipulator endl causes the cursor to

move to beginning of the next line.


Escape Sequences in Output Statements

• Escape sequences are another way to format output. Example: The new line character is '\n'

cout << "Hello there."; cout << "My name is James."; Output:Hello there.My name is James.

cout << "Hello there.\n"; cout << "My name is James."; Output :Hello there.My name is James.


Escape Sequences in Output Statements (cont’d.)


The Standard Library

• The core C++ language has a relatively small number of built-in operations.

• Many other useful operations are provided as a collection of files called the C++ Standard Library.

• These library files make your job easier, because they save you from having to re-invent the wheel when you want to perform common tasks.

• A big part of becoming a C++ programmer is learning about the many library files in the Standard Library.


The Standard Library (cont’d.)

• Each library file (or “header file”) has a name, which is typically written inside angle brackets.– Examples:

• <iostream>• <string>• <cmath>

• The next slides show how to tell the compiler that you want to use operations from one or more of these files.


Preprocessor Directives

• Your programs will often contain preprocessor directives. These are commands that the preprocessor program executes before your program is compiled.

• All preprocessor directives begin with #.

• No semicolon at the end of these directives.


The #include Directive

• The most common preprocessor directive is #include, which is how you tell the compiler that you want to use a Standard Library file.

• Syntax to include a header file:

• For example:#include <iostream>

– Causes the preprocessor to include the header file iostream in the program. Without this, you could not use cout or cin in your program.


namespace and Using cin and cout in a Program

• cin and cout are declared in the header file iostream, but within the std namespace.

• To use cin or cout in a program, use the following two statements:#include <iostream>using namespace std;

• Without that using statement, you would need to type std::cin instead of cin throughout your program.


Using the string Data Type in a Program

• Recall that the string data type is not built into the core C++ language. It’s a programmer-defined type defined in the C++ Standard Library.

• To use the string type, you need to access its definition from the header file string.

• Use the following preprocessor directive:#include <string>


The main Function

• A function is a named block of code that performs some well-defined set of operations.

• Every C++ program must contain a function named main. This is where execution begins when you run the program.

• Complex programs contain many functions, but for now most of your programs will only contain the main function.


The main Function (cont’d.)

• The first line of a function is called the function’s heading: int main()

• The statements enclosed between the curly braces { and } form the function’s body.


Named Constants

• Named constant: memory location whose content cannot change during execution.

• Syntax to declare a named constant:

• By convention, constant identifiers are all upper-case.


Syntax Errors

• Syntax rules: indicate what is legal and what is not legal.– Example of a syntax rule: Every C++ statement

must end with a semicolon.• The compiler finds and reports syntax errors during

compilation. It won’t let you run the program until you fix these errors.int x; //Line 1int y //Line 2: Syntax error


Semantic Errors

• Semantic rules: set of rules that gives meaning to a language.

• A program with no syntax errors may still not produce correct results.

• Example: 2 + 3 * 5 and (2 + 3) * 5are both syntactically correct expressions, but have different meanings. So if you use one of these expressions where you should use the other one, your program will produce incorrect results.


Prompt Lines

• Prompt lines are statements that tell the user what to do.

cout << "Please enter a number between 1 and 10 and " << "press the return key." << endl;cin >> num;

• Always include a prompt line when you want the user to enter some input.


Documentation

• A well-documented program is easier to understand and modify.

• Two keys to good documentation:1. Use comments.2. Choose meaningful variable names.

• Comments should:– Explain the purpose of the program.– Identify who wrote it, and when.– Explain the purpose of particular statements whose

meaning is not obvious.


Documentation (cont’d.)

• Variable names should be self-documenting:– Example: use CENTIMETERS_PER_INCH instead of X.

• Avoid run-together words, such as annualsale. This is hard to read.– Solution:

• Either capitalize the beginning of each new word: annualSale

• Or insert an underscore just before a new word: annual_sale


Compound Assignment Statements

• In addition to the simple assignment operator =, C++ provides several compound assignment operators, including: += -= *= /= %=

• Simple assignment statement:x = x * y;

• Equivalent compound assignment statement:x *= y;

• Their sole purpose is to provide more concise notation. But you don’t need to use them.


egr 2261 unit 2 basic elements of c++ read malik, chapter 2. homework #2 and lab #2 due next week....

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