[C language] what is a function? Classification and emphasis of functions (help you quickly classify and remember functions)

One ： What is a function ？

   We often see the concept of function in Mathematics , But you know C Functions in language ？
Wikipedia definition of function ： Subroutines

• In computer science , Subroutines （ English ：subroutine、procedure、function、routine、method、subprogram、callable uint）, It's a piece of code in a large program , Consists of one or more statement blocks . It is responsible for completing a specific task , And compared to other code , With relative independence .
• Generally, there are input parameters and return values , Provide encapsulation of the process and hiding of details . These codes are often referred to as software libraries .

Two ：C Classification of functions in language ？

1. Library function

1.1 Why are there library functions ？

   Such as scanf、printf、strlen Wait, we all often use , Functions implemented by compiler manufacturers that play a certain function , Called library functions . And such as ,VS The library function of is provided by Microsoft ,gcc Library functions for are gcc Official supply ,clang The library function of is provided by apple, etc . All in all , Library functions we will often use , To avoid unnecessary trouble , Provided by the manufacturer , The function we use is called library function .

1.2 Classification of library functions ？

Classification of functions , A brief summary ,C The library functions commonly used in language are ：

• IO function
• String manipulation functions
• Character manipulation functions
• Memory manipulation function
• Time / Date operation function
• Mathematical functions
• Other library functions

1.3 How to learn to use library functions ？

Do you need to remember all the library functions ？ The answer is ：No！

This is the age of the Internet , We just need to have an impression , I know this function in my mind , Then you can query and use . Now I recommend some tools for querying library functions ：

• MSDN(Microsoft Developer Network), This is a library function query software used by an internal employee of Microsoft .
• cpp research Website （ recommend , Very easy to use , Friends with poor English can download a translation plug-in ）
• http://en.cppreference.com( English version )
• http://ch.cppreference.com( Chinese version )
  Tips： English is very important , You should at least barely understand the literature .

2. Custom function

If the library function can do anything , What else should programmers do ？

therefore , For us , More importantly, custom functions , We can also define functions in library functions . Custom functions are the same as library functions , There's a function name , Return type , Function parameter . The difference is that this is designed by us , This gives us a lot of room to play , Have you figured out how to do your own function ？

I think , friend , You don't want to go whoring for nothing ？