C-language functions, function calls and function recursion

1. Function definition: Return value type function name (formal parameter list) {function body (Implementation content of function)}, note: Parentheses are also necessary if there are no arguments.

A call can be nested between functions and functions (that is, you can call another function inside a function), but you cannot nest definitions (you cannot define another function within one function)

Formal parameters: In the case of a function definition, the given parameter is called the formal parameter, and is a variable that stores the data before the call is complete.

Argument: The parameter given when a function call is called an argument is a uniquely determined data. The process of passing an argument to a parameter is a copy of the process

function is equivalent to the company's department, each part of the completion of a specific function, department and Department of the side-by-side relationship between function and function is also a side relationship

Function: Implement the modular management of the code. The complex logic is split, and the main function is only the function of macro-control, the main functions are the entrance of application execution

Errors that may occur during function definition:

A. function definition is not a allowed here: Reason: A new function is defined inside the function, nested definition

Solution: The function is a side-by-side relationship that defines the internally defined function externally

B. Control reaches end of non-void function: Reason: The return value cannot be null, the function does not return data through return

Solution: Returns the corresponding data by return

2. function definition form:

A. function definition first form : no parameter , no return value

void Buymike () {

printf(" no money Yet");

　　　　}

naming conventions for function names : There are more than one English barbed , except for the first letter in lowercase , the remaining words are capitalized

B. Second form of function definition : Return value , no parameter

Float salary () {

printf(" comrades have done a good job this year, good work next year, do not job-hopping \ \");

return 1.0;//ruturn Returns the value of the function to the keynote function

//Do not put the code below the return , will not be executed

}

c. Third form of function definition : No return value , parameter

void BuyMike2 (float money) {

if (Money < ) {

printf (" not enough money \ \");

} Else {

printf("OK, buy milk \ n");

}

}

　　D. The fourth form of the function definition : There is a return value , there are parameters

Maximum value for two numbers

int maxvalueoftwo (int A, int b) {

return a > B? a:b;

}

　　　　To find the minimum value of two numbers

int minvalueoftwo (int A, int b) {

return a < b? a:b;

}

　　　　Maximum value for three numbers

int Maxofthreenumber (int A, int b, int c) {

1. Max for a and b first

int max = 0;// Store maximum value

max = Maxvalueoftwo (A, b);

2. Max vs . c Max

return maxvalueoftwo(Maxvalueoftwo(A, B), c);

}

3. Function call (let function work)

A. function with no return value: function name (pass the argument table); such as BuyMike2 (3.2);

B. function with return value: Defines a variable corresponding to the return value type used to receive the value returned by the function call. such as: int max = MaxValue (2, 3);

4. Array and function of the relationship, array as the parameters of the function:

A. When an array is a function parameter, only the function name is passed as int a[10] = {0}; Outputarray (A, ten);//outputarray (int arr[], int n) is a function of its own definition

5. The use of functions is divided into three parts :(in Xcode)

A. function declaration , similar to the instruction manual , written in the . h file

B. function definition (Implementation of function ), implementation written in . m file

c. function invocation ( The import header file is essentially a copy of the contents of the . h file into the file )

6. Scope of variables : range of variables accessible

　　Local variables : variables defined inside the function are called local variables , are accessible only inside the function, space is created when the function executes , and the function execution end space is automatically recycled

　　Global variables : variables defined outside the function are called global variables , accessible globally , and space is not recycled (warning: Global variables are dangerous , use caution )

Static variable : any variable that is modified by static is called a static variable .

features: 1. If the initial value is not assigned, the default is 0

2. Initialize only once ( the variable is defined only once)

3. Once the space is opened, it will not be recycled

7. Function recursion: The recursive function is to invoke a function that is exactly the same as the function (note: Recursion must have an exit , otherwise it will cause a dead loop ), such as:

　　

Function Simulation eating apples

void Eatapple (int n) {

//Once the number of apples is found to be 0, end the current function execution by return

Recursion must have an exit , otherwise it will cause a dead loop.

if (n = = 0) {

return; // return null

}

if it is not zero

1. Keep an apple

n--;

2. find the next person to eat an apple

eatapple (n);

3. eat the apples in your own hands

printf (" %d person eats apples : \ n", 10-n);

}

function calls are made directly in the main function: Eatapple (ten);

Reverse 54321

　　void reverse (int n) {

if (n = = 0) {

return;

}

1. number of left

int m = n% ;

2. Count off

printf ("%d", m);

3. find the next one.

reverse (n/ ten);

}

Positive Order

void positive (int n) {

if (n = = 0) {

return;

}

1. number of left

int m = n% ;

2. find the next one.

positive (n/ ten);

3. Count off

printf ("%d", m);

}

factorial

int FAC (int n) {

if (n = = 0 | | n = = 1) {//0 and 1 have a factorial of 1

return 1;

}

return n * FAC (n- 1);

}

C-language functions, function calls and function recursion