C language programming (Chapter 6 functions)

C Language programming （ Chapter six function ）

1、 Why define functions

Defining functions includes the following ：

（1） Specify the name of the function , To call by name later .

（2） Specifies the type of function , That is, the type of function return value .

（3） Specifies the name and type of the function's arguments , To pass data to functions when they are called . This is not required for nonparametric functions .

（4） Specifies what the function should do , That is, what a function does , The function of a function . That's the most important thing , It is solved in the function body .

2、 How to define a function

（1） Define nonparametric functions

 Type name   Function name (){
    
	 The body of the function 
}

 or 

 Type name   Function name (void){
    
	 The body of the function 
}

#include<stdio.h>
int main(){
    
	void print_star();
	void print_message();
	print_star();
	print_message();
	print_star();
	return 0;
}
void print_star(){
    
	printf("*******************\n");
}
void printf_message(){
    
	printf("Hello,world!\n");
}

 Execution results :
*******************
Hello,world!
*******************

（2） Define parametric function

As defined below max Function is a parametric function ：

 Type name   Function name ( Formal parameter table column ){
    
     The body of the function 
}

int max(int x,int y){
    
	int z;
	z=x>y?x:y;
	return(z);
}

（3） Define empty functions

 Type name   Function name (){
    
	
}

 for example :
void dummy(){
    

}

3、 Call function

（1） The form of function call

 The general form of a function call is 
 Function name ( Argument table column )

print_star();         // Call parameterless function 
c=max(a,b);			  // Call the parameter function 

（2） Function call statements

Take the function call as a single statement , The function is not required to bring back the value , Only the function is required to complete certain operations . for example ：

print_start();

(3) Function expression

The function call appears in another expression , Such as “c=max(a,b);”,max(a,b) It's a function call , It's part of the assignment expression . At this time, the function is required to bring back a certain value to participate in the operation of the expression . for example ：

c=2*max(a,b);

(4) Function parameter

The argument when a function call is used as another function call . for example ：

m=max(a,max(b,c));

4、 Function call data transfer

（1） Formal parameters and actual parameters

​ Calling There are parametric functions when , There is a data transfer relationship between the calling function and the called function . Known from the front ： When defining a function, the variable name in parentheses after the function name is “ Formal parameters ”（ abbreviation “ Shape parameter ”） or “ Virtual parameters ”. When calling a function in the keynote function , The arguments in parentheses after the function name are called “ The actual parameter ”（ abbreviation “ Actual parameters ”）. The actual parameter can be a constant 、 Variable or expression .

（2） Data transfer between arguments and formal parameters

In the process of calling the function , The system will pass the value of the argument to the formal parameter of the called function .

Example 1： Enter two integers , The larger value is required to be output . It requires a function to find a large number .

#include<stdio.h>
int max(int x,int y){
    
    int z;
    z=x>y?x:y;
    return(z);
}

int main(){
    
    int max(int x,int y);
    int a,b,c;
    printf(" Please enter two integers :");
    scanf("%d%d",&a,&b);
    c=max(a,b);
    printf("max is %d\n",c);
    return 0;
}

 Execution results :
 Please enter two integers :18 48
max is 48

（3） The return value of the function

① The return value of the function is passed through return The statement gets .

② The type of function value

③ When defining a function, the specified function type should be similar to return The expression types in statements are the same , That is, the function type determines the type of the return value .

④ For functions not brought back , The function should be defined as “void type ”（ Or called “ Empty type ”）

5、 Nested calls to functions

Example 2： Input 4 It's an integer , Find the largest number . Use the nesting of functions to deal with .

#include<stdio.h>
int main(){
    
    int max4(int a,int b,int c,int d);
    int a,b,c,d,max;
    printf(" Please enter 4 A digital :");
    scanf("%d%d%d%d",&a,&b,&c,&d);
    max=max4(a,b,c,d);
    printf("max is %d\n",max);
    return 0;
}
int max4(int a,int b,int c,int d){
    
    int max2(int a,int b);
    int m;
    m=max2(a,b);
    m=max2(m,c);
    m=max2(m,d);
    return m;
}
int max2(int a,int b){
    
    if(a>=b){
    
        return a;
    }
    else 
        return b;
}

 Execution results :
 Please enter 4 A digital :43 65 6 8
max is 65

6、 Recursive call of function

In the process of calling a function, it occurs to call the function itself directly or indirectly , Called recursive calls to functions .

Example 3： Find... Recursively n！

#include<stdio.h>
int main(){
    
    int fac(int n);
    int n,y;
    printf(" Please enter the number of factorials ：");
    scanf("%d",&n);
    y=fac(n);
    printf("%d!=%d\n",n,y);
    return 0;
}

int fac(int n){
    
    int f;
    if(n<0){
    
        printf("n<0,data Error!");
    }
    if(n==0 || n==1){
    
        f=1;
    }
    else{
    
        f=fac(n-1)*n;
    }
    return f;
}

 Execution results :
 Please enter the number of factorials ：10
10!=3628800

Example 4： The hanotta problem

#include<stdio.h>
int main(){
    
    void hanoi(int n,char one,char two,char three);
    int m;
    printf(" Please enter the number of plates ：");
    scanf("%d",&m);
    printf("%d Plate movement ：\n");
    hanoi(m,'A','B','C');
    return 0;
}

void hanoi(int n,char one,char two,char three){
    
    void move(char x,char y);
    if(n==1){
    
        move(one,three);
    }
    else{
    
        hanoi(n-1,one,three,two);
        move(one,three);
        hanoi(n-1,two,one,three);
    }
}


void move(char x,char y)
{
    
    printf("%c->%c\n",x,y);
}

7、 One dimensional array name as function parameter

Example 5： There's a one-dimensional array score, Place... Inside 10 Students' grades , For the average score

#include<stdio.h>
int main(){
    float average(float array[10]);
    float score[10],aver;
    int i;
    printf(" Please enter 10 Scores of students ：\n");
    for(i=0;i<=9;i++){
        scanf("%f",&score[i]);
    }
    aver=average(score);
    printf("average score is %5.2f\n",aver);
    return 0;
}

float average(float array[10]){
    int i;
    float aver,sum=0;
    for(i=0;i<=9;i++){
        sum+=array[i];
    }
    aver=sum/10;
    return aver;
}

 Execution results :

 Please enter 10 Scores of students ：
100 56 78 98 67.5 99 54 88.5 76 58
average score is 77.50

8、 Multidimensional array name as function parameter

Example 6： There is one 3×4 Matrix , Find the maximum of all elements

#include<stdio.h>
int main(){
    
    int max(int array[][4]);
    int a[3][4]={
    {
    1,3,5,7},{
    2,4,6,8},{
    12,13,17,14}};
    printf("max value is %d\n",max(a));
    return 0;
}

int max(int array[][4]){
    
    int i,j,max;
    max=array[0][0];
    for(i=0;i<3;i++){
    
        for(j=0;j<4;j++){
    
            if(array[i][j]>max){
    
                max=array[i][j];
            }
        }
    }
    return max;
}

 Execution results :
max value is 17