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Chapter 2 Introduction to C++ Programming C++, How to Program Deitel & Deitel

Learn C++ by Examples Five examples demonstrate How to display messages How to obtain information from the user How to perform arithmetic calculations

Important Parts of a C++ program Comments: //, /* …. */ Preprocessor directives : #include Function main Body of the function Return statement Other statements

Comments Explain programs to other programmers Improve program readability Ignored by compiler Single-line comment Begin with // Example // allows program to output data to the screen . Multi-line comment Start with /* End with */

Preprocessor Directives Preprocessor directives Processed by preprocessor before compiling Begin with # Example #include <iostream> Tells preprocessor to include the input/output stream header file <iostream> White space s Blank lines, space characters and tabs Delimiter, used to make programs easier to read Extra spaces are ignored by the compiler

Function main A part of every C++ program Exactly one function in a program must be main main is a Keyword. Keyword : A word in code that is reserved by C++ for a specific use. Header of function main : int main( ) Body is delimited by braces ( { } )

Statements Instruct the program to perform an action All statements end with a semicolon ( ; ) Examples : return 0; std::cout << “Welcome to C++!\n ”;

return Statement One of several means to exit a function When used at the end of main The value 0 indicates the program terminated successfully Example return 0;

Output Statement (1) std::cout << “Welcome to C++!\n”; std::cout Standard output stream object . Defined in input/output stream header file <iostream> We are using a name ( cout ) that belongs to “namespace” std . Norm ally outputs to computer screen . Stream insertion operator << Value to right (right operand) inserted into left operand . The string of characters contained between “ ” after the operator << shows on computer screen.

Output Statement (2) Escape character : backslash : " \ " Escape sequence : A character preceded by backslash ( \ ) Indicates “special” character output Example s : "\n" Newline. Cursor moves to beginning of next line on the screen “ \t” Horizontal tab. Move the screen cursor to the next tab stop.

Good Programming Practices Add comments Every program should begin with a comment that describes the purpose of the program, author, date and time. Use good indentation Indent the entire body of each function one level within the braces that delimit the body of the function. This makes a program’s functional structure stand out and helps make the program easier to read.

Run C++ Program Save the program with the right extension programOne.cpp Send the program in the right directory Compiling the program: g++ programOne.cpp –o programOne.out Run the executable file ./programOne.out

Modifying Our First C++ Program Print text on one line using multiple statements Each stream insertion resumes printing where the previous one stopped Statements: Std::cout << “Welcome ”; Std::cout << “to C++!\n”;

Modifying Our First C++ Program Print text on several lines using a single statement . Each newline escape sequence positions the cursor to the beginning of the next line Two newline characters back to back outputs a blank line Example statement : Std::cout << “Welcome \n to \n\n C++! \n ”;

Variable Location in memory where value can be stored Common data types (fundamental, primitive or built-in) int – integer numbers : 1, 2, 4,…. char – characters : ‘a’, ‘c’, … float, double – floating point numbers: 2.5, 4.96 The value of a variable could be changed while the program is running.

Declaration of Variables (1) Declare variables with name and data type before they are use d. A variable name is any valid identifier that is not a keyword. Series of characters - letters, digits, underscores ( _ ) Cannot begin with digit Case sensitive Choosing meaningful identifiers helps make a program self-documenting .

Declaration of Variables (2) Can Declare each variable on a separate line. int integer1; int integer2; int sum; Can declare several variables of same type in one declaration . Comma-separated list int integer1, integer2, sum;

Assign Value to Variables Assignment operator = Assigns value on right to variable on left Binary operator (two operands) Assign a value after declaration int integer1; //declaration integer1 = 10; //assignment Declare and assign a value at the same time. int integer2 = 20;

Input stream object std::cin from <iostream> Usually connected to keyboard Stream extraction operator >> Waits for user to input value, press Enter (Return) key Stores value in variable to right of operator Converts value to variable data type Example int number1; std::cin >> number1; Reads an integer typed at the keyboard Stores the integer in variable number1

Constant variables Declared using the const qualifier Also called named constants or read-only variables Must be initialized with a constant expression when they are declared and cannot be modified thereafter Example: const int size = 5;

Arithmetic (1) Arithmetic operators + : Addition - : Subtraction * : Multiplication / : Division Integer division truncates remainder 7 / 5 evaluates to 1 % : Modulus operator returns remainder 7 % 5 evaluates to 2 Attempting to use the modulus operator ( % ) with non - integer operands is a compilation error.

Arithmetic (2) Straight-line form Required for arithmetic expressions in C++ All constants, variables and operators appear in a straight line Grouping sub - expressions Parentheses are used in C++ expressions to group sub - expressions Same manner as in algebraic expressions Example a * ( b + c ) Multiple a times the quantity b + c

Rules of operator precedence Operators in parentheses evaluated first Nested/embedded parentheses Operators in innermost pair first Multiplication, division, modulus applied next Operators applied from left to right Addition, subtraction applied last Operators applied from left to right

Precedence of Arithmetic Operators

Performing Arithmetic Calculation in C++ Program Adding two integers int number1, number2, sum; std::cin >> number1; std::cin >> number2; sum = number 1 + number 2; Add the values of variable1 and variable2 Store result in sum

Question Question : int integerOne = 1; double doubleOne = 2.5; int sumOne = integerOne + doubleOne; //A double sumTwo = integerOne + doubleOne; //B Which statement is correct , A or B ?

Output Statement With Expression Variables or expressions could be inserted into output statement, its value is printed out. Long output statement could be broken into multiple lines. Example: std::cout << “sum is ” << sum << “. bye-bye! \n”; std::cout << “sum is ” << number1 + number2 ;

End of Line Stream manipulator std::endl Outputs a newline Flushes the output buffer

Memory Concepts Variable names Correspond to actual locations in computer's memory Every variable has name, type, size and value When new value placed into variable, overwrites old value Writing to memory is destructive Reading variables from memory nondestructive Example sum = number1 + number2; Value of sum is overwritten Values of number1 and number2 remain intact

Fig. 2.6 | Memory location showing the name and value of variable number1.

Fig. 2.7 | Memory locations after storing values for number1 and number2.

Fig. 2.8 | Memory locations after calculating and storing the sum of number1 and number2.

Type Sizes and Ranges The size and range of any data type is compiler and architecture dependent. M any architectures implement data types of a standard size. ints and floats are often 32-bit, chars 8-bit, and doubles are usually 64-bit.

Reference Reproduced from the Cyber Classroom for C++, How to Program , 5/e by Deitel & Deitel. Reproduced by permission of Pearson Education, Inc.

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