Preprocessor Directives and Object Oriented Programming | CSE A205, Study notes of Engineering

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CSE294A

Introduction to C Programming for Engineers

Lecture

Jeffrey Miller, Ph.D.

Preprocessor Directives

Preprocessing occurs before a program iscompiled

Preprocessor directives begin with a

Only whitespace characters and comments mayappear before a preprocessor directive on a line

#define Preprocessor Directive

The #define preprocessor directive is used to createsymbolic constants

#define identifier replacement-text

When a #define is used, all subsequent occurrences of theidentifier that appear outside of string literals are replacedby the replacement-text automatically before the programis compiled

The values of variables are not evaluated in preprocessordirectives because they are evaluated prior to the codebeing compiled

#define PI 3.

#define Proprocessor Directive

The #define preprocessor directive can be used to definemacros

A macro is similar to a function, but the macro will beexpanded in-line in the program when it is called #define PI 3.14159 #define

CIRCLE_AREA(x)

(PI)

(x)

(x)) ... area = CIRCLE_AREA(4); // expanded to: area

Conditional Preprocessor Directives

Conditional preprocessor directives enable you to control the execution ofother preprocessor directives and the compilation of program code - #ifdef is used to determine if a preprocessor directive has been defined - #ifndef is used to determine if a preprocesor directive has not been defined - #endif is used to denote the end of the conditional preprocessor directive - NOTE: This is often used when including header files that have classes defined, which issomething you will learn in the object-oriented programming class next semester #ifndef DEBUG #define DEBUG - #endif

Object-Oriented Programming

C is not an object-oriented language, though C++ is - C++ is a superset of C, meaning that anything you cando in C you can also do in C++

But C++ can do more!

In C, the closest construct we have to object-orientation is structures, which logically groupvariables together - In C++, a object (which is an instance of a class) hasboth variables and functions

Class Implementation

// in a file called Bank_Account.cpp #include “Bank_Account.h” Bank_Account::Bank_Account(double bal, int acct, char* name) { balance = bal; account_number = acct; strcpy(customer_name, name); } void Bank_Account::deposit(double amount) { balance += amount; } void Bank_Account::withdraw(double amount) { balance -= amount; } double Bank_Account::check_balance() { return balance; }

Using a Class

#include “Bank_Account.h” void main() { Bank_Account ba1(2000.30, 1234, “jeff”); Bank_Account ba2(3000.40, 2345, “mike”); ba1.deposit(1000.00); ba2.withdraw(2000.00); printf (“ba1 balance = %.2lf\n”, ba1.check_balance()); printf (“ba2 balance = %.2lf\n”, ba2.check_balance()); }

Homework

Homework #8 is posted!