Functions in c++
- A function is a subroutine that contains one or more C++ statements and performs a specific task.
- Every program that you have written so far has used one function: main( ).
- They are called the building blocks of C++ because a program is a collection of functions.
- All of the “action” statements of a program are found within functions.
- Thus, a function contains the statements that you typically think of as being the executable part of a program.
- A function has a name and a type, much like a variable. The function’s type is defined by its return value, that is, the value the function passes back to the program.
- In addition, the type of arguments required by a function is important. When a function is declared, the compiler must therefore be provided with information on
- the name and type of the function and
- the type of each argument.
double pow(double, double);
This informs the compiler that the function toupper() is of type int, i.e. its return value is of type int, and it expects an argument of type int.
The second function pow() is of type double and two arguments of type double must be passed to the function when it is called.
The types of the arguments may be followed by names, however, the names are viewed as a comment only.
- The definition consists of a line called the declarator, followed by the function body.
- The function body is composed of the statements that make up the function, delimited by braces.
void starline() //declarator
for(int j=0; j<45; j++) //function body
cout << ‘*’;
cout << endl;
Passing Pointers to Functions
- To pass a pointer as an argument, you must declare the parameter as a pointer type.
// Pass a pointer to a function.
using namespace std;
void f(int *j);
cout << i;
void f(int *j)
*j =100; //var pointed to by j is assigned 100
Passing an Array
- When an array is an argument to a function, the address of the first element of the array is passed, not a copy of the entire array. (Recall that an array name without any index is a pointer to the first element in the array.)
- This means that the parameter declaration must be of a compatible type.
//Pass a pointer to a function.
using namespace std;
void display(int num);
int t, t;
for(i=0; i<10; ++t)
display(t); // pass array t to a function
//Print some number.
void display(int num) // Parameter declared as a sized array
for(i=0; i <10; i++)
cout << num[i] << ' ';