This chapter is from the book
This chapter is from the book
This chapter is from the book
Functions in C++
Functions in C++ are the same as functions in C. Functions are artifacts that enable you to divide the content of your application into functional units that can be invoked in a sequence of your choosing. A function, when called (that is, invoked), typically returns a value to the calling function. The most famous function is, of course, main(). It is recognized by the compiler as the starting point of your C++ application and has to return an int (i.e., an integer).
You as a programmer have the choice and usually the need to compose your own functions. Listing 2.4 is a simple application that uses a function to display statements on the screen using std::cout with various parameters.
Listing 2.4. Declaring, Defining, and Calling a Function That Demonstrates Some Capabilities of std::cout
1: #include <iostream>
2: using namespace std;
3:
4: // Function declaration
5: int DemoConsoleOutput();
6:
7: int main()
8: {
9: // Call i.e. invoke the function
10: DemoConsoleOutput();
11:
12: return 0;
13: }
14:
15: // Function definition
16: int DemoConsoleOutput()
17: {
18: cout << "This is a simple string literal" << endl;
19: cout << "Writing number five: " << 5 << endl;
20: cout << "Performing division 10 / 5 = " << 10 / 5 << endl;
21: cout << "Pi when approximated is 22 / 7 = " << 22 / 7 << endl;
22: cout << "Pi more accurately is 22 / 7 = " << 22.0 / 7 << endl;
23:
24: return 0;
25: }
Output
This is a simple string literal Writing number five: 5 Performing division 10 / 5 = 2 Pi when approximated is 22 / 7 = 3 Pi more accurately is 22 / 7 = 3.14286
Listing 2.5. Using the Return Value of a Function
1: #include <iostream>
2: using namespace std;
3:
4: // Function declaration and definition
5: int DemoConsoleOutput()
6: {
7: cout << "This is a simple string literal" << endl;
8: cout << "Writing number five: " << 5 << endl;
9: cout << "Performing division 10 / 5 = " << 10 / 5 << endl;
10: cout << "Pi when approximated is 22 / 7 = " << 22 / 7 << endl;
11: cout << "Pi more accurately is 22 / 7 = " << 22.0 / 7 << endl;
12:
13: return 0;
14: }
15:
16: int main()
17: {
18: // Function call with return used to exit
19: return DemoConsoleOutput();
20: }
Functions can take parameters, can be recursive, can contain multiple return statements, can be overloaded, can be expanded in-line by the compiler, and lots more. These concepts are introduced in greater detail in Lesson 7, “Organizing Code with Functions.”