Basic Elements of C++ Chapter 1

Chapter Topics The Basics of a C++ Program Data Types Arithmetic Operators and Operator Precedence Expressions Input Increment and Decrement Operators Output Preprocessor Directives Program Style and Form More on Assignment Statements

The Basics of a C++ Program A C++ program is a collection of one or more subprograms (functions) Function Collection of statements Statements accomplish a task Every C++ program has a function called main

Welcome to C++ Programming Example Program #include <iostream> using namespace std; int main() { cout<<"Welcome to C++ Programming"<<endl; return 0; } Welcome to C++ Programming Program Output

#include <iostream> using namespace std; int main() { cout << "Hello World!" << endl; return 0; }

#include <iostream> using namespace std; int main() { // A simple C++ program int x, y, sum; cout << "A program which adds two integers\n"; cout << "Enter 1st integer: "; cin >> x; cout << "Enter 2nd integer: "; cin >> y; sum = x + y; cout << "Sum is " << sum << endl; return 0; }

#include <iostream> using namespace std; int main() { int i; // i is an integer variable. float x; // x is a floating-point variable. char c; // c is a character variable. x = 4.7; // 4.7 is assigned to x. cout << x << endl; i = x + 2.1; // 6 (after truncating the fractional part of ... cout << i << endl; // ... 6.8) is assigned to i. c = 81; // The character with ASCII code 81 ('Q') is ... cout << c << endl; // ... assigned to c. The character is 'Q'. i = 'b'; // The ASCII code of 'b' (98) is assigned to i. cout << i << endl; return 0; }

The Basics of a C++ Program Programming language a set of rules, symbols, special words Rules syntax – specifies legal instructions Symbols special symbols ( + - * ! … ) Word symbols reserved words (int, float, double, char …)

Identifiers Rules for identifiers Evaluate the following must begin with letter or the underscore _ followed by any combination of numerals or letters recommend meaningful identifiers Evaluate the following ElectricCharge 23Skidoo Operator in C++ Operation Sample C++ expression Equivalent Pascal expression + Addition p + q - Subtraction m - n * Multiplication a * b /  Division x / y x div y (if both x and y are of integer types) x / y (if at least one operand is of floating point type) % Modulus r % s r mod s

Data Types Definition: a set of values combined with a set of operations

Data Types Simple data types include Integer data types include Integers Floating point Enumeration Integer data types include char short int long bool Numerals, symbols, letters Numbers without decimals Values true and false only

Floating-Point Types Stored using scientific notation the sign of the number, the significant digits of the number the sign of the power of 10 the power of 10

Data Types Different floating- point types Note that various types will have different ranges of values require different amounts of memory

Data Types The string Type A string is a sequence of characters a programmer-defined type requires #include <string> A string is a sequence of characters "Hi Mom" "We're Number 1!" "75607"

Arithmetic Operators and Operator Precedence Common operators for calculations + - * / % Precedence same as in algebraic usage Inside parentheses done first Next * / % from left to right Then + and - from left to right Note operator precedence chart, page 1035

Expressions An expression includes constants variables function calls combined with operators 3 / 2 + 5.0 sin(x) + sqrt(y)

Expressions Expressions can include values all of the same type 3 + 5 * 12 – 7 values of different (compatible) types 1.23 * 18 / 9.5 An operation is evaluated according to the types of the operands if they are the same, the result is the type of the operands if the operands are different (int and float) then the result is float

Type Casting Implicit change of type can occur when operands are of different type It is possible to explicitly specify that an expression be converted to a different type static_cast < type > (expression) static_cast <int> (3.5 * 6.9 / x)

Input Storing data in the computer's memory requires two steps Allocate the memory by declaring a variable Have the program fetch a value from the input device and place it in the allocated memory location cin >> x 123 x

Note optional initialization of the variable Allocating Memory Variable A memory location whose content may change during program execution Declaration: Syntax: type identifier; Example: double x; int y = 45; Note optional initialization of the variable

Note required initialization of the named constant Allocating Memory Named Constant A memory location whose content cannot be changed Declaration Syntax: const type identifier = value; Example const double PI = 3.14159; Note required initialization of the named constant

Putting Data Into Variables At initialization time Assignment statement Syntax: variable = expression; Example x = 1.234; volume = sqr (base) * height; Input (read) statement Syntax: cin >> variable ; Example cin >> height; Program Example

Increment and Decrement Operators Pre-increment ++x; equivalent to x = x + 1; Pre-decrement --x; Changes the value before execution of a statement y = ++x; Post-increment intVal++; Post-decrement intVal--; Changes the value after execution of the statement y = x++;

Manipulator for carriage return Output Values sent to an output device Usually the screen Can also be a file or some device Syntax for screen output: cout << expression << … Example cout << "The total is "<< sum << endl; Insertion operator Manipulator for carriage return Output command Values to be printed Sample Program

Output Escape sequences also used to manipulate output cout << "The total is\t "<< sum << endl;

Preprocessor Directives Commands supplied to the preprocessor Runs before the compiler Modifies the text of the source code before the compiler starts Syntax start with # symbol #include <headerFileName> Example #include <iostream>

Preprocessor Directives Note the preprocessor step in the sequence

Namespace The #include <iostream> command is where cin and cout are declared They are declared within a namespace called std When we specify using namespace std; Then we need not preface the cin and cout commands with std::cin and std::cout

Program Style and Form Every program must contain a function called main int main (void) { … } The int specifies that it returns an integer value The void specifies there will be no arguments Also can say void main( ) { … }

Program Style and Form Variables usually declared inside main at beginning of program Use blanks and space to make the program easy for humans to read Semicolons ; required to end a statement Commas used to separate things in a list

Program Style and Form Documentation Comments specified between /* this is a comment */ and following // also a comment Always put at beginning of program /* name, date, cpo, purpose of program */

Program Style and Form Names of identifiers should help document program double electricCharge; // instead of ec Prompt keyboard entry cout << "Enter the value for x -> "; cin >> x;

Example 1 #include <iostream> using namespace std; int main( ) { int numberOfLanguages; cout << "Hello reader.\n" << "Welcome to C++.\n"; cout << "How many programming languages have you used? "; cin >> numberOfLanguages; if (numberOfLanguages < 1) cout << "Read the preface. You may prefer\n" << "a more elementary book by the same author.\n"; else cout << "Enjoy the book.\n"; system("pause"); return 0; }

Example 2 #include <iostream> // Required for cout, endl. #include <cmath> // Required for sqrt() using namespace std; int main() { // Declare and initialize objects. double x1(1), y1(5), x2(4), y2(7), side1, side2, distance; // Compute sides of a right triangle. side1 = x2 - x1; side2 = y2 - y1; distance = sqrt(side1*side1 + side2*side2); // Print distance. cout << "The distance between the two points is " << distance << endl; // Exit program. system("pause"); return 0; }

// my first program in C++ #include <iostream> int main() { std::cout << "Hello World!"; }

// my second program in C++ #include <iostream> int main () { std::cout << "Hello World! "; std::cout << "I'm a C++ program"; } In one line int main () { std::cout << " Hello World! "; std::cout << " I'm a C++ program "; }

Comments Comments 1 2 // line comment /* block comment */ As noted above, comments do not affect the operation of the program; however, they provide an important tool to document directly within the source code what the program does and how it operates. C++ supports two ways of commenting code: 1 2 // line comment /* block comment */

/* my second program in C++ with more comments */ #include <iostream> int main () { std::cout << "Hello World! "; // prints Hello World! std::cout << "I'm a C++ program"; // prints I'm a C++ program }

Using namespace std Using namespace std If you have seen C++ code before, you may have seen cout being used instead of std::cout. Both name the same object: the first one uses its unqualified name (cout), while the second qualifies it directly within the namespace std (as std::cout). cout is part of the standard library, and all the elements in the standard C++ library are declared within what is a called a namespace: the namespace std. In order to refer to the elements in the std namespace a program shall either qualify each and every use of elements of the library (as we have done by prefixing cout with std::), or introduce visibility of its components. The most typical way to introduce visibility of these components is by means of using declarations: using namespace std

// my second program in C++ #include <iostream> using namespace std; int main () { cout << "Hello World! "; cout << "I'm a C++ program"; }

Variables and types The usefulness of the "Hello World" programs shown in the previous chapter is rather questionable. We had to write several lines of code, compile them, and then execute the resulting program, just to obtain the result of a simple sentence written on the screen. It certainly would have been much faster to type the output sentence ourselves. However, programming is not limited only to printing simple texts on the screen. In order to go a little further on and to become able to write programs that perform useful tasks that really save us work, we need to introduce the concept of variable. Let's imagine that I ask you to remember the number 5, and then I ask you to also memorize the number 2 at the same time. You have just stored two different values in your memory (5 and 2). Now, if I ask you to add 1 to the first number I said, you should be retaining the numbers 6 (that is 5+1) and 2 in your memory. Then we could, for example, subtract these values and obtain 4 as result. The whole process described above is a simile of what a computer can do with two variables. The same process can be expressed in C++ with the following set of statements: a = 5; b = 2; a = a + 1; result = a - b;

a = 5; b = 2; a = a + 1; result = a - b;

#include <iostream> using namespace std; int main() { int a; int b; cout<<"Enter first number:\n"; cin >> a; cout <<"Enter the second number:\n"; cin>> b; int result = a + b; cout<<"Result is"<<" "<<result<<endl; return 0; }

#include <iostream> #include <string> using namespace std; int main () { string s; cout << "jhun \n" ; cin >> s; cout << "Hello, " << s << '\n' ; return 0; // this return statement isn't necessary }

#include <iostream> using namespace std; int main() { cout << "Hello World!" << endl; return 0; } */ #include <cmath> int x = 0; while(x < 10) { double y = sqrt((double)x); cout << "The square root of " << x << " is " << y << endl; x++;