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Object oriented programming 11 preprocessor directives and program structure
- 1. Object Oriented Programming: 11 Preprocessor Directives and Program Structure in C++ Prof Neeraj Bhargava Vaibhav Khanna Department of Computer Science School of Engineering and Systems Sciences Maharshi Dayanand Saraswati University Ajmer
- 2. 2 Preprocessor Directives • C++ has a small number of operations • Many functions and symbols needed to run a C++ program are provided as collection of libraries • Every library has a name and is referred to by a header file • Preprocessor directives are commands supplied to the preprocessor • All preprocessor commands begin with # • No semicolon at the end of these commands
- 3. 3 Preprocessor Directives (continued) • Syntax to include a header file: • For example: #include <iostream> – Causes the preprocessor to include the header file iostream in the program
- 4. 4 namespace and Using cin and cout in a Program • cin and cout are declared in the header file iostream, but within std namespace • To use cin and cout in a program, use the following two statements: #include <iostream> using namespace std;
- 5. 5 Using the string Data Type in a Program • To use the string type, you need to access its definition from the header file string • Include the following preprocessor directive: #include <string>
- 6. 6 Creating a C++ Program • C++ program has two parts: – Preprocessor directives – The program • Preprocessor directives and program statements constitute C++ source code (.cpp) • Compiler generates object code (.obj) • Executable code is produced and saved in a file with the file extension .exe
- 7. 7 Creating a C++ Program (continued) • A C++ program is a collection of functions, one of which is the function main • The first line of the function main is called the heading of the function: int main() • The statements enclosed between the curly braces ({ and }) form the body of the function – Contains two types of statements: • Declaration statements • Executable statements
- 8. 8
- 9. 9 Creating a C++ Program (continued) Sample Run: Line 9: firstNum = 18 Line 10: Enter an integer: 15 Line 13: secondNum = 15 Line 15: The new value of firstNum = 60
- 10. 10 Program Style and Form • Every C++ program has a function main • It must also follow the syntax rules • Other rules serve the purpose of giving precise meaning to the language
- 11. 11 Syntax • Errors in syntax are found in compilation int x; //Line 1 int y //Line 2: error double z; //Line 3 y = w + x; //Line 4: error
- 12. 12 Use of Blanks • In C++, you use one or more blanks to separate numbers when data is input • Used to separate reserved words and identifiers from each other and from other symbols • Must never appear within a reserved word or identifier
- 13. 13 Use of Semicolons, Brackets, and Commas • All C++ statements end with a semicolon – Also called a statement terminator • { and } are not C++ statements • Commas separate items in a list
- 14. 14 Semantics • Possible to remove all syntax errors in a program and still not have it run • Even if it runs, it may still not do what you meant it to do • For example, 2 + 3 * 5 and (2 + 3) * 5 are both syntactically correct expressions, but have different meanings
- 15. 15 Naming Identifiers • Identifiers can be self-documenting: – CENTIMETERS_PER_INCH • Avoid run-together words : – annualsale – Solution: • Capitalize the beginning of each new word – annualSale • Inserting an underscore just before a new word – annual_sale
- 16. 16 Prompt Lines • Prompt lines: executable statements that inform the user what to do cout << "Please enter a number between 1 and 10 and " << "press the return key" << endl; cin >> num;
- 17. 17 Documentation • A well-documented program is easier to understand and modify • You use comments to document programs • Comments should appear in a program to: – Explain the purpose of the program – Identify who wrote it – Explain the purpose of particular statements
- 18. 18 Form and Style • Consider two ways of declaring variables: – Method 1 int feet, inch; double x, y; – Method 2 int a,b;double x,y; • Both are correct; however, the second is hard to read
- 19. 19 More on Assignment Statements • C++ has special assignment statements called compound assignments +=, -=, *=, /=, and %= • Example: x *= y;
- 20. Assignment • What is the role of preprocessor directives in C++ • Describe the general structure of a C++ program using an example program