C++ Functions

C++ Functions ”; Previous Next A function is a group of statements that together perform a task. Every C++ program has at least one function, which is main(), and all the most trivial programs can define additional functions. You can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division usually is such that each function performs a specific task. A function declaration tells the compiler about a function”s name, return type, and parameters. A function definition provides the actual body of the function. The C++ standard library provides numerous built-in functions that your program can call. For example, function strcat() to concatenate two strings, function memcpy() to copy one memory location to another location and many more functions. A function is known with various names like a method or a sub-routine or a procedure etc. Defining a Function The general form of a C++ function definition is as follows − return_type function_name( parameter list ) { body of the function } A C++ function definition consists of a function header and a function body. Here are all the parts of a function − Return Type − A function may return a value. The return_type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the keyword void. Function Name − This is the actual name of the function. The function name and the parameter list together constitute the function signature. Parameters − A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters. Function Body − The function body contains a collection of statements that define what the function does. Example Following is the source code for a function called max(). This function takes two parameters num1 and num2 and return the biggest of both − // function returning the max between two numbers int max(int num1, int num2) { // local variable declaration int result; if (num1 > num2) result = num1; else result = num2; return result; } Function Declarations A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately. A function declaration has the following parts − return_type function_name( parameter list ); For the above defined function max(), following is the function declaration − int max(int num1, int num2); Parameter names are not important in function declaration only their type is required, so following is also valid declaration − int max(int, int); Function declaration is required when you define a function in one source file and you call that function in another file. In such case, you should declare the function at the top of the file calling the function. Calling a Function While creating a C++ function, you give a definition of what the function has to do. To use a function, you will have to call or invoke that function. When a program calls a function, program control is transferred to the called function. A called function performs defined task and when it’s return statement is executed or when its function-ending closing brace is reached, it returns program control back to the main program. To call a function, you simply need to pass the required parameters along with function name, and if function returns a value, then you can store returned value. For example − Live Demo #include <iostream> using namespace std; // function declaration int max(int num1, int num2); int main () { // local variable declaration: int a = 100; int b = 200; int ret; // calling a function to get max value. ret = max(a, b); cout << “Max value is : ” << ret << endl; return 0; } // function returning the max between two numbers int max(int num1, int num2) { // local variable declaration int result; if (num1 > num2) result = num1; else result = num2; return result; } I kept max() function along with main() function and compiled the source code. While running final executable, it would produce the following result − Max value is : 200 Function Arguments If a function is to use arguments, it must declare variables that accept the values of the arguments. These variables are called the formal parameters of the function. The formal parameters behave like other local variables inside the function and are created upon entry into the function and destroyed upon exit. While calling a function, there are two ways that arguments can be passed to a function − Sr.No Call Type & Description 1 Call by Value This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. 2 Call by Pointer This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. 3 Call by Reference This method copies the reference of an argument into the formal parameter. Inside the function, the reference is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. By default, C++ uses call by value to pass arguments. In general, this means that code within a function cannot alter the arguments used to call the function and above mentioned example while calling max() function used the same method. Default Values for Parameters When you define a function, you can specify a default value

C++ Abstraction

Data Abstraction in C++ ”; Previous Next Data abstraction refers to providing only essential information to the outside world and hiding their background details, i.e., to represent the needed information in program without presenting the details. Data abstraction is a programming (and design) technique that relies on the separation of interface and implementation. Let”s take one real life example of a TV, which you can turn on and off, change the channel, adjust the volume, and add external components such as speakers, VCRs, and DVD players, BUT you do not know its internal details, that is, you do not know how it receives signals over the air or through a cable, how it translates them, and finally displays them on the screen. Thus, we can say a television clearly separates its internal implementation from its external interface and you can play with its interfaces like the power button, channel changer, and volume control without having any knowledge of its internals. In C++, classes provides great level of data abstraction. They provide sufficient public methods to the outside world to play with the functionality of the object and to manipulate object data, i.e., state without actually knowing how class has been implemented internally. For example, your program can make a call to the sort() function without knowing what algorithm the function actually uses to sort the given values. In fact, the underlying implementation of the sorting functionality could change between releases of the library, and as long as the interface stays the same, your function call will still work. In C++, we use classes to define our own abstract data types (ADT). You can use the cout object of class ostream to stream data to standard output like this − Live Demo #include <iostream> using namespace std; int main() { cout << “Hello C++” <<endl; return 0; } Here, you don”t need to understand how cout displays the text on the user”s screen. You need to only know the public interface and the underlying implementation of ‘cout’ is free to change. Access Labels Enforce Abstraction In C++, we use access labels to define the abstract interface to the class. A class may contain zero or more access labels − Members defined with a public label are accessible to all parts of the program. The data-abstraction view of a type is defined by its public members. Members defined with a private label are not accessible to code that uses the class. The private sections hide the implementation from code that uses the type. There are no restrictions on how often an access label may appear. Each access label specifies the access level of the succeeding member definitions. The specified access level remains in effect until the next access label is encountered or the closing right brace of the class body is seen. Benefits of Data Abstraction Data abstraction provides two important advantages − Class internals are protected from inadvertent user-level errors, which might corrupt the state of the object. The class implementation may evolve over time in response to changing requirements or bug reports without requiring change in user-level code. By defining data members only in the private section of the class, the class author is free to make changes in the data. If the implementation changes, only the class code needs to be examined to see what affect the change may have. If data is public, then any function that directly access the data members of the old representation might be broken. Data Abstraction Example Any C++ program where you implement a class with public and private members is an example of data abstraction. Consider the following example − Live Demo #include <iostream> using namespace std; class Adder { public: // constructor Adder(int i = 0) { total = i; } // interface to outside world void addNum(int number) { total += number; } // interface to outside world int getTotal() { return total; }; private: // hidden data from outside world int total; }; int main() { Adder a; a.addNum(10); a.addNum(20); a.addNum(30); cout << “Total ” << a.getTotal() <<endl; return 0; } When the above code is compiled and executed, it produces the following result − Total 60 Above class adds numbers together, and returns the sum. The public members – addNum and getTotal are the interfaces to the outside world and a user needs to know them to use the class. The private member total is something that the user doesn”t need to know about, but is needed for the class to operate properly. Designing Strategy Abstraction separates code into interface and implementation. So while designing your component, you must keep interface independent of the implementation so that if you change underlying implementation then interface would remain intact. In this case whatever programs are using these interfaces, they would not be impacted and would just need a recompilation with the latest implementation. Print Page Previous Next Advertisements ”;

C++ Encapsulation

Data Encapsulation in C++ ”; Previous Next All C++ programs are composed of the following two fundamental elements − Program statements (code) − This is the part of a program that performs actions and they are called functions. Program data − The data is the information of the program which gets affected by the program functions. Encapsulation is an Object Oriented Programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse. Data encapsulation led to the important OOP concept of data hiding. Data encapsulation is a mechanism of bundling the data, and the functions that use them and data abstraction is a mechanism of exposing only the interfaces and hiding the implementation details from the user. C++ supports the properties of encapsulation and data hiding through the creation of user-defined types, called classes. We already have studied that a class can contain private, protected and public members. By default, all items defined in a class are private. For example − class Box { public: double getVolume(void) { return length * breadth * height; } private: double length; // Length of a box double breadth; // Breadth of a box double height; // Height of a box }; The variables length, breadth, and height are private. This means that they can be accessed only by other members of the Box class, and not by any other part of your program. This is one way encapsulation is achieved. To make parts of a class public (i.e., accessible to other parts of your program), you must declare them after the public keyword. All variables or functions defined after the public specifier are accessible by all other functions in your program. Making one class a friend of another exposes the implementation details and reduces encapsulation. The ideal is to keep as many of the details of each class hidden from all other classes as possible. Data Encapsulation Example Any C++ program where you implement a class with public and private members is an example of data encapsulation and data abstraction. Consider the following example − Live Demo #include <iostream> using namespace std; class Adder { public: // constructor Adder(int i = 0) { total = i; } // interface to outside world void addNum(int number) { total += number; } // interface to outside world int getTotal() { return total; }; private: // hidden data from outside world int total; }; int main() { Adder a; a.addNum(10); a.addNum(20); a.addNum(30); cout << “Total ” << a.getTotal() <<endl; return 0; } When the above code is compiled and executed, it produces the following result − Total 60 Above class adds numbers together, and returns the sum. The public members addNum and getTotal are the interfaces to the outside world and a user needs to know them to use the class. The private member total is something that is hidden from the outside world, but is needed for the class to operate properly. Designing Strategy Most of us have learnt to make class members private by default unless we really need to expose them. That”s just good encapsulation. This is applied most frequently to data members, but it applies equally to all members, including virtual functions. Print Page Previous Next Advertisements ”;