Functions in C++
In C++ a function is a program unit which encapsulates a sequence of instructions aimed at accomplishing a particular function. It is also a set of instructions that make any desired computation benefits hitherto given benefits of writing once and calling many times in the program. Functions provide many advantages over non-booked code including program understandable, avoid duplication of code, debugging capability is enhanced, and others.
C++ functions can be described in their most basic form as having three parts:
1. Function Declaration (or Prototype):
This specifies the name of the function, the data type that is returned by the function, and the parameters of the function. It explains to the compiler the type of data that the function will receive and the type of value that the function will return. The declaration of the function comes before the function is invoked or used in a program.
2. Function Definition:
It gives the name of the function and its body. There in the body of the function, the mentioned operations or tasks are conducted. It comes later the declaration and executes the logic of the particular task that is overridden by the function.
3. Function Call:
It is during this part that the function is implemented into the program. The function call enables the program to hand over control to the function defined and once the function is executed with all its tasks, returns back the control to the point from which it was invoked.
Every C++ function may return a number, an alphabet, or a float, besides the integer values, and if the function does not return anything, it could also be declared void. Furthermore, a function is capable of receiving parameters, which allow it to be given certain values to perform its operation, enabling it to complete a particular task. In this way, the functions can be regarded as aid for the development of complex programs by dividing the jobs into several smaller ones.
Parameters and Arguments
In C++, functions need some input in order to work as they should. For clients using XSI or any X software, that input is done through parameters, which are defined when a certain function is erected. Parameters are variables that will be replaced by actual values (arguments) when the function gets executed. It means that a single function can be executed multiple times with different parameters.
Filling in the gaps left by the parameters, the duties of the arguments are to create the actual function bodies. Where else, the values of these parameters can afterwards be incorporated into the functions themselves.
Scope in C++
The definition of a variable range in a program’s part is called scope. It decides the extent to which a variable can be accessed and altered. In C++, there are different types of scope which are Local scope, global scope and function scope.
1. Local Scope:
The term ‘local scope’ refers to parameters, variables and data that are declared within a function. It means that the local variables can only be accessed within that function and from nowhere else. This implies that as soon as the function ends its execution, the data in such variables is deleted and cannot be used, since its value is lost. Local variables are also useful for storing data that are needed only for some parts of the program or local functions.
2. Global Scope:
A variable declared outside any function probably at the beginning of the program is said to be of global scope. A global variable is one that can be used from anywhere, that is from all the functions of the program. These variables are in the scope all over the program and their scope lasts from the time the program starts until it terminates. However, it is recommended that they should not be used as much as possible otherwise the program becomes so difficult to comprehend and maintain.
3. Function Scope:
All variables which are declared within a function have function scope which makes them accessible only from that given function. These variables come into existence as the function gets invoked and cease to exist when the function is completed and executed. They are independent of outer functions, that is, two functions can declare variables with the same name without any conflict between them.
4. Block Scope:
Variables can have a block scope which means that they can only be used within the specific block of code in which they were defined. A block of code is indicated by a pair of curly braces, `{ }`. The scope of such variables will be restricted only within that block, and on exiting this block, they cannot be used. This is very common in loops and in conditional statements.
C++ Scope and Local Variable
In the case of C++, whenever one has to call a function, a separate scope is formed for that particular function. This means that all variables that are defined inside the function’s body are only defined and fully accessible within the body of that function. These variables are defined as local variables and they hold a primary importance in modifying, structuring or controlling the flow of data within the program.
As an example, consider a case where a particular function has two parameters and the function performs some calculation using those parameters. Thus the parameters will be in existence only during the lifetime of the function. After the function is done, the lifetime for the local variables which are the parameters in this case ends, so all these parameters and their values are permanently destroyed or inaccessible.
The way the local variables are in a particular scope is helpful in ensuring that they do not affect or mix up with other segments of the program. Since it is hidden from the eyes of the rest of the program there are no chances of other parts of the program trying to alter the data and this is how it is useful. It also helps to promote a modular pattern in which each function works independently.
Global Variables and Their Scope
The code is well-structured and does not have any conflicts because of the presence of local variables. But on some occasions, it might be required to share a variable across multiple functions. In such situations, one can make use of global variables. Global Variable refers to all the variables which are declared outside any function, generally at the beginning of the program. A global variable is visible and may be changed by any function within the program.
Even though global variables have their advantages, global variables also have their disadvantages. If global variables are used too often it may prove a program to be confused and also hard to maintain as one might not know the exact location in which a global variable is changed. Hence global variables should be used sparingly and with care as it can result in bugs that may be hard to debug.
