Introduction to Functions
A function in C++ contains a set of instructions that are executed when it is called.
A function declaration is composed of three parts:
- Function return type
- Function name
- Function parameters
A function can be called by specifying its name followed by a pair of parentheses ().
#include <iostream>
void printTitle() {
std::string msg = "Codecademy\n";
std::cout << msg;
}
int main(){
printTitle();
return 0;
}
Function Parameters
When calling a function with multiple parameters, the number and order of the arguments must match with the parameters.
Default parameters initialize to a default value if an argument is not provided in the function call.
Pass by reference lets the function modify the arguments variables. Use the & operator to indicate that a parameter is passed by reference.
#include <iostream>
double totalPrice(int items, double price = 9.99) {
return items * price;
}
// Pass by reference
void addOne(int &i) {
i += 1;
}
int main() {
std::cout << totalPrice(10) << "\n"; // Output: 99.9
int num = 2;
addOne(num);
std::cout << num; // Output: 3
return 0;
}Function Overloading
With function overloading, C++ functions can have the same name but handle different input parameters.
At least one of the following criteria must be true in order for functions to be properly overloaded:
- Each function has different types of parameters.
- Each function has a different number of parameters.
The function return type is NOT used to differentiate overloaded functions.
#include <iostream>
int add(int a, int b) {
return a + b;
}
double add(double a, double b) {
return a + b;
}
int add(int a, int b, int c) {
return a + b + c;
}
int main() {
std::cout << add(3, 2); // Calls add(int, int)
std::cout << "\n";
std::cout << add(5.3, 1.4); // Calls add(double, double)
std::cout << "\n";
std::cout << add(2, 6, 9); // Calls add(int, int, int)
}Command Line Arguments
Command line arguments are optional arguments passed to the main() function of a C++ program.
Passing command line arguments is as easy as appending the arguments after the executable name. For example:
In order to access command line arguments, the new form of main() takes two arguments:
argc: the number of command line arguments.argv: an array containing the values of command line arguments.
#include <iostream>
int main(int argc, char* argv[]) {
std::cout << argc << "\n";
for(int i = 0; i < argc; i++) {
std::cout << argv[i] << "\n";
}
return 0;
}