08-c language Functions

First, what is a function

L any C language program is composed of one or more program segments (small programs), each of which has its own function, which we generally call "functions". So, you can say that the C language program is composed of functions.

L For example, if you write a MP3 player program in C, the program structure is as follows:

Second, the definition of function 1. Defining the purpose of a function

L encapsulate a common function to make it easy to call 2 later. Steps to define a function

L Function Name: What is the function name

L function Body: What does the function do, and what code 3 is included in it. Format

L fixed format (all functions in many languages are written in this way)

return value type function name (formal parameter list)

{

function body

}

l Example

Defines a function that calculates the number of two integers and

sum (int a, int b)

{

int C = a + B;

} third, function call

L SUM (10, 11); Elicit return value

L Description of Function call procedure

L briefly describe the function of return iv. parameters of functions

1. Basic concepts of formal parameters and arguments

2. The number of formal parameters and arguments are the same: sum (10, 11, 12)

3. The pass of a parameter is a value pass

4. Parameter names cannot have the same name as local variables within a function

5. Functions can have no parameters: Design a function return pi five, function return value

1. The basic concept of the return value, the role of return

2. void

3. Return

l void can omit return

L can use return multiple times

L cannot have other statements after return

4. Weak syntax for functions

L If there is no write return value type, the default is int

L If you write a return value, you can not return

L Call a function that has not been defined six, the steps to define a function

1. Clear function, a meaningful function name

2. Define the parameters and return values of the function

3. For example:

L to ask for two integers and

L Print a horizontal line

L Print N horizontal line seven, function note

L cannot nest defined functions

L Call myself in a dead loop.

L cannot repeat the definition, can repeat the declaration eight, the function of the Supplement 1. Main function

L return Value: 0, normal exit, 1, abnormal exit 2. printf function

L #include

L return Value: Length of string nine, exercise

1. Write a function double AVR (int a, int b) to calculate the average of A and B

2. Write a function int POWs (int base, int n) to return the n-th square of the base

3. Write a function int pieadd (int n), calculate the value of the 1+2+3+......+n and return. For example, the return value of Pieadd (3) is 1+2+3=6 10, the declaration of the function

1. The order in which functions are defined

2. function declaration function: Declaration and definition, similar to the identity card and human Relations, the compilation of buy tickets, link boarding

3. Only function declaration, no definition, compilation warning, link Error xi.,. h file and. C File Division

1. The disadvantages of a single file

L The contents of a file are too many, not conducive to reading, debugging

L Multiple people modify the same file problem

L The company is a team player.

2. Extract the sum function into another. c file

L CALL the SUM function directly first, compile warning, link MAIN.C error

L #include "sum.c", compile link main.c, run successfully (Paint analysis. o file)

L if SUM.C is used in avr.c, compile the link main.c, run the program (the reason for drawing analysis error)

3. Declaring the SUM function in other files

l int sum (int,int);

L Compile Link main.c

L Compile Link sum.c

L Compile link main.c sum.c, run successfully

L AVR.C Use the same method

4. Extract int sum (int,int) to another file

L Do not extract the disadvantages of the declaration: Add a new function

L extract to. c file? The development tool will compile all the. C Links

L extract to. h file

5. Summary of extraction Steps

L. c file definition of write function

L. h file Write function declaration

If you want to use my function, please include my. h file

L Benefit Analysis 12, #include 1. Introduction to preprocessing Directives 2. #include的作用

is purely a file copy of 3. #include <stdio.h>

L What's in stdio.h? What to do when it comes to linking

L <> and "" The Difference 4. #include的路径问题

L The default is the same path, other issues are discussed later

08-c language Functions