Default Arguments

Default Arguments

C++ lets you give parameters a default value. If the caller doesn't supply that argument, the default is used.

Syntax

void greet(string name, string greeting = "Hello") {
    cout << greeting << ", " << name << "!" << endl;
}

greet("Alice");          // Hello, Alice!
greet("Bob", "Hi");      // Hi, Bob!
greet("Carol", "Hey");   // Hey, Carol!

Rules

• Defaults must be at the end of the parameter list
• Once a parameter has a default, all following parameters must too

// Valid
void f(int a, int b = 2, int c = 3);

// Invalid — non-default after default
void g(int a = 1, int b, int c = 3);  // error

Mixing Required and Optional Parameters

string repeat(string text, int times = 3, string sep = ", ") {
    string result = "";
    for (int i = 0; i < times; i++) {
        if (i > 0) result += sep;
        result += text;
    }
    return result;
}

cout << repeat("ha") << endl;              // ha, ha, ha
cout << repeat("go", 2) << endl;           // go, go
cout << repeat("x", 4, "-") << endl;       // x-x-x-x

When to Use Default Arguments

Use defaults when a parameter has a sensible common value that most callers would want. They reduce the need for overloads in simple cases.

Your Task

Write a greet function that takes a name and an optional greeting (default "Hello"), and a multiply function that takes a and optional b (default 2), returning a * b.

Call them as shown to produce the expected output.