C language Learning-functions and recursive functions

C source program is composed of functions, and there is only one main function (main () function).

First, the function

1. The writing format of the Custom function:

返回值类型 函数名(参数类型 形式参数1，参数类型 形式参数2，…){    函数体}
For example:

1Include <stdio.h>2 voidtest ();3 4 intMain () {5 test ();6     return 0;7 }8 9 voidTest () {Ten  Oneprintf"Hello world!");  A  -}

2. Purpose of defining functions

Encapsulates a function to make it easier to call later

3. Steps to define a function

Function name: What are the names of functions?

Function Body: What does the function do and what code it contains

Return value type: What is returned to the caller after the function has finished executing

4. Definition of no parameter, no return value function

Format:

void function name () {

function body;

}

For example:

void say () {      printf (" speak up, how you are! ");}

5. Definition of a function with a return value without a parameter
Format:

return value type function name () {

function body;

}

For example:

int sum () {    return;  }

6. The definition of a parameter without a return value function

Format:

void function name (parameter type form parameter 1, parameter type parameter 2 ...) {

function body;

}

For example:

1 void printline (int  n) {2     int1;         3      while (I <= n) {4          printf ("---------"); 5          i++; 6     }   7     8 }

7. Parameters have the definition of a return value function

Format:

return value type function name (parameter type parameter 1, parameter type parameter 2 ...) {

function body;

}

For example:

1 int sum (intint  b) {2     return  a + b; 3 }

Second, recursive function

A function calls itself in its function body called a recursive call. This function is called a recursive function. The C language allows recursive invocation of functions. In recursive invocation, the keynote function is also the function of the tune. Executing a recursive function calls itself repeatedly, entering a new layer each time it is called.

void function (int  x) {    function (x);}

• themselves call themselves
• There is a condition that allows recursion to end
• The scale of the problem can be reduced

For example:

Gets the number entered by the user until the user enters a positive

1 voidInputnumber ()2 {3     intNumber =-1;4printf"Please enter a positive number abc\n");5scanf"%d", &Number );6     if(Number <0) {7 //Negative number8 Inputnumber ();9}Else{Ten //Positive Oneprintf"Number =%d\n", number); A     } -}

Using recursion to find the factorial of n

1 intFactorial (intN) {2     intresult =0;//define the result of variables used to hold factorial3     if(n==1) {//if the n=1, 1! The result is still 1 .4result =1;5}Else{6result = Factorial (n1) *n;//if not 1, factorial = (n-1)!*n;7     }8     returnresult;9}

C language Learning-functions and recursive functions