What are functions for?

A function in mathematics is a correspondence between two sets: each element of a set of input values corresponds to an element of a unique set of output values. For example, the relationship of a real number x to its square x? is a function; if 3 is the input value of this function, the output value is 9.

Partial image of the function f. Each real number x is related to f by an equation. Each real number of x is associated with f(x) =?x 9x.

Given a set of numbers A, suppose that the elements in it are x. Now apply the correspondence law f, denoted f(x), to the elements x in A to obtain another set of numbers B. Suppose that the elements in B are y. The equivalence between y and x can be expressed as y = f(x). We call this relation a functional relation, or function for short. The concept of function contains three elements: the domain of definition A, the domain of value C, and the law of correspondence f. At the center of this is the law of correspondence f, which is the essential feature of the functional relation.

Function was first translated by Li Shanlan, a mathematician in the Qing Dynasty of China, in his book Algebra. The reason he gave for this translation was that "where this variable contains a function of another variable, this is a function of that variable," meaning that a function is a quantity that varies as another quantity varies, or a quantity that contains another quantity. The definition of the function is usually divided into traditional definition and recent definition, the two definitions of the function of the essence of the same, just recounting the concept of the starting point is different, the traditional definition is from the point of view of the change of the movement, while the recent definition is from the point of view of the set, mapping.

Programming

These statements in a function procedure are used to accomplish some meaningful work - usually processing text, controlling input, or calculating values. The function can be executed (or called) within that program by introducing the name of the function and the required arguments in the program code.

Similar to procedures, though functions generally have a return value. They can all call themselves inside their own structure, called recursion.

Most programming languages include the function keyword (or reserved word) in their method of constructing functions.

Functions in Programming

In many programming languages, it is possible to encapsulate a piece of code that you need to use frequently, so that you can call it directly when you need to use it. For example, in C:

int max(int x,int y)

{

return(x>y?x:y;);

}

It's a function that compares the size of two numbers, with parameters and a return value.Functions in C++ can be classified into two categories: functions with parameters and functions without parameters. These two types of parameters are declared and defined differently.

Declaration of a function with (one) parameter:

Type name identifier + function name + (type identifier + parameter)

{

// Program code

}

Declaration of a function with no return value and no parameter:

void+function name ()

{

{

// Program code

Declaration of a function without return value and without parameter:

Void+function name ()

{

// Program code

}

The body of the function is enclosed in curly braces.

If there is no return value the type name is "void", int type return value is int, and so on ......

Type names are: void int long float int* long* float* ... ...

Calling functions in C++: Functions must be declared before they can be called. The call format is: function name (real parameter)

The real parameter in parentheses after the function name must be the same as the number of formal parameter in parentheses when the function is declared.

Functions with a return value can be computed and can also be made right-valued for assignment.

#include <iostream>

using namespace std;

int f1(int x, int y)

{int z;

return x+y;

}

void main()

{cout<<f1(50,660)<<endl

}

Some of the functions in C

main

max (the main function)

max (the function to find the maximum number)

canf (the input function)

rintf (output function)

gets (standard input stream function)

Library Functions in C Language

C language in order to facilitate the user to write programs for the user to develop a large number of library functions, which are defined in the .h file, the user can call these functions to achieve powerful functions. So for the user to master the usage of these functions is the key to improve the level of programming.