Parameters
- C++ course
- Beginner
- Lesson 67/116
- 4 min
Learn to pass parameters to a function.
Parameter and argument
A function can take values from outside. In the definition you write a parameter: name in void greet(std::string name) is a parameter. The value you pass at the call is an argument: "Alex" in greet("Alex") is an argument.
The parameter behaves like a local variable inside the function. At call time the argument's value is copied into the parameter; this is called call by value. So even if you change the parameter inside the function, the caller's original variable is unaffected.
Call by value
The default behavior in C++ is call by value. When you call void addTen(int x) with addTen(n), the value of n is copied into x. Even if you write x = x + 10;, n stays the same.
This limits side effects and makes code easier to follow. If you want the function to modify the caller, you need a reference parameter; we cover that in a later level. For now, knowing parameters are copies is enough.
Practice Write parameterized greet and call it
Define a void greet(std::string name) function whose body is std::cout << "hi " << name << std::endl;. In main, call greet("Alex").
Starter code
#include <iostream>
#include <string>
// Define greet here
int main() {
// greet call (argument: Alex)
return 0;
}Sample solution
#include <iostream>
#include <string>
void greet(std::string name) {
std::cout << "hi " << name << std::endl;
}
int main() {
greet("Alex");
return 0;
}Expected output
hi Alex
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Match parameter and argument
| Term | Meaning |
|---|---|
void greet(std::string name) |
Definition |
greet("Alex") |
Call |
name |
Parameter |
"Alex" |
Argument |
2 After calling void inc(int x) { x++; }, what is n? (n = 5)
int n = 5;
inc(n);- Compile error
- n becomes undefined
- n becomes 6
- n stays 5 Correct answer
Explanation: in call by value the copy of n changes, n itself stays 5.
3 Complete the parameterized function
void greet(std::string ____) { std::cout << name; }void greet(std::string name) { std::cout << name; }Explanation: the name parameter is used in the body.