Some summary about function

One ： Function call procedure

1. Memory space ： Defining formal parameters in a function , When there is no function call , They do not occupy memory storage units , When a function call occurs , function max When the formal parameter of is zero, the memory unit is allocated .

2. The transmission of value ： Pass the value corresponding to the argument to the formal parameter , Parameter values for 2, hold 2 Pass to the corresponding formal parameter , Then the formal parameter gets the formal parameter x Get the value 2, Formal parameters get values 3.

3. Worth returning ： adopt return Statement to bring the value of the function back to the main function , In the following code , The specified return value is z, This is the of the function max Value （ Also called return value ）. perform return Statement brings the return value of this function back to the calling function main, It should be noted that the type of the return value is the same as the function type . Such as max Function is int type , A variable that returns a value z, It's also int type , Two to the same .

#include <stdi#include <stdio.h>
int getMaxFromData(int x,int y){
    
    int sum;
	if(x>y)
	{
    
		z=x;
	}else	
    {
    
		z=y;
	}
	return z;
}

int main()
{
    
    int data1;
	int data2;
	int bigOne;
    
	printf(" Please enter two numbers ：\n");
	scanf("%d%d%d",&data1,&data2);
	bigOne=getMaxFromData(data1,data2);
	printf(" The two numbers you enter are ：%d,%d\n",data1,data2);
	printf(" The largest of these two numbers is %d, The smallest is %d\n",bigOne);
	
	printf("\t Program end ！");
    return 0;
}

4. Memory free ： At the end of the call , The parameter unit is released . Be careful *** The argument unit retains and maintains its original value , There is no change , If when executing a called function , The value of formal parameter changes , Does not change the value of the argument of the calling function . such as ： If it's executing max In the process of function ,x and y The value of a 10 and 15, but a and b Still 2 and 3; This is because the real participation parameter is two different storage units .

#include <stdio.h>
int test(int x)
{
    
	printf("test Function x The memory storage address is ：%p, Values are ：%d\t",&x,x);
	int y;
	return y;
	
}



int main()
{
    
    int x;
	int y;
	printf(" Please enter a number ：\n");
	scanf("%d",&x);
	printf("main Function x The memory storage address is ：%p, Values are ：%d\n",&x,x);
	y=test(x);
    return 0;
}

Two ： Condition of function call

1. Function has been defined

2. Call library function ： If you use library functions , It should be used at the beginning of this document #include The instruction includes the information needed to call the relevant library functions in this document , Columns such as , Instructions that have been used in previous chapters

#include <stdio.h>

among “stdio.h” It's a header file . stay stdio.h The file contains the declaration of input and output library functions . If not “stdio.h” Information in the file , You cannot use functions in the input / output library , Also use the functions in the math library , Should use the ：

#include <math.h>

h Is the suffix used in the header file , Indicates that it is a header file ,（header fire）