default parameter

default parameter

What is a default parameter?

on a typical morning,you want to buy a milk tea,so you open your smartphone,and select your favorate flavor.After a monent,you decide to pay for it.At this point,your smartphone usually has options to let you choose sugar level.If you don't make a selection,your milk tea will be made with full sugar-this is just like a default parameter in programming.

How to use default parameter

Basic grammar

int add(int a=10,int b=10){
//if you don't pass any parameter,the fuction use a=10 and b=10 default
return a+b;
}

simple program block

int add(int a=1, int b=1) {
	return a + b;
}

int main() {
	int a, b;
	cout << "Enter values for a and b(default:1 if not entered)：";
	cin >> a >> b;
	cout<<add()<<endl;              //Call without parameter
 	cout << add(a, b) << endl;          //Call with parameters
}

output

Enter values for a and b(default:1 if not entered)：1 2
2
3

Points to note

1. Default parameters can only be specified in the function declaration (not repeated in the definition)

int add(int a=10,b=10)
int main(...){...}

int add(int a=10,b=10)   //Invalid
//👇
int add(int a,b)         //Valid

2. Default parameters must be placed at the end of the parameter list

int add(int a=10,b)      //Invalid
//👇
int add(int b,a=10)      //Valid

3. use constant and #define macros instead of assigning values to variables

#define s 10
int b=1;
int function(int a=s)         //👍
int function(int a=1)         //👍
int function(int a=b)         //❌

this is all,thank you for reading