Formal parameters, local variables and local static variables

Formal parameters and variables defined inside the function body are collectively referred to as local variables , They are local to functions , Visible only in the scope of a function . The local variables in the function body are divided into ordinary local variables and static local variables , For formal parameters and ordinary local variables , This object is created when the control path of a function passes through a variable definition statement , Destroy the definition when it reaches the end of the block . We call objects that exist only during block execution automatic objects . Of these concepts difference yes :

• A formal parameter is an automatic object , The function starts by applying memory for a parameter , We initialize the automatic object corresponding to the formal parameter with the arguments provided when calling the function .
• Automatic objects corresponding to common variables are also easy to understand , We create an automatic object at the statement that defines the variable , If the definition statement provides an initial value , Then initialize with this value ; otherwise , Perform default initialization . When the block where the variable is located ends , Variable failure .
• Local static variables are special , Its life cycle runs through function calls and beyond . The object corresponding to a local static variable is called a local static object , Its life cycle starts at the definition statement , Not until the end of the program .

Code help ：

#include<iostream>
using namespace std;
double myAdd(double val1,double val2){
	double resul = val1+val2;
	static unsigned iCnt = 0;// Static local variables （ Throughout the process ）
	++iCnt;
	cout<<" This function performs a total of "<<iCnt<<" Time "<<endl;
	return resul;
}

int main(){
	double num1,num2; // Ordinary local variables 
	cout<<" Please enter two numbers ："<<endl;
	while(cin>>num1>>num2){
		cout<<" The sum result is ："<<myAdd(num1,num2)<<endl; 
	}
	return 0;
}

Output results ：

 Please enter two numbers ：
2.4
3.4
 This function performs a total of 1 Time 
 The sum result is ：5.8
33
33
 This function performs a total of 2 Time 
 The sum result is ：66
43
34
 This function performs a total of 3 Time 
 The sum result is ：77
^Z
 Please press any key to continue . . .