C++ lecture 03

Functions
 Functions allow to structure programs in segments of code to
perform individual tasks.
 It is a group of statements that is given a name, and which can be
called from some point of the program.
 The most common syntax to define a function is:
type name ( parameter1, parameter2, ...)
{
statements
}

 type - the type of the value returned by the
function.
 Name - the identifier by which the function can be
called.
 Parameters -The purpose of parameters is to allow
passing arguments to the function from the location
where it is called from.
 Statements - the function's body. It is a block of
statements surrounded by braces { } that specify
what the function actually does.
Functions

Example
int addition (int a, int b)
{
int r;
r=a+b;
return r;
}
int main () {
int z;
z = addition (5,3);
cout << "The result is " << z;
}
Type
Name
Parameter
Statements

Explanation
 The final statement within the function:
return r;

int subtraction (int a, int b) {
int r;
r=a-b;
return r;
}
int main () {
int x=5, y=3, z;
z = subtraction (7,2);
cout << "The first result is " << z << 'n';
cout << "The second result is " << subtraction
(7,2) << 'n';
cout << "The third result is " << subtraction
(x,y) << 'n';
z= 4 + subtraction (x,y);
cout << "The fourth result is " << z << 'n'; }

Functions with no return type
// void function example
#include <iostream>
using namespace std;
void printmessage () {
cout << "I'm a function!";
}
int main () {
printmessage ();
}

Arguments passed by value
 when calling a function, the values of the arguments on
the moment of the call, which are copied into the variables
represented by the function parameters.
 For example, take:
int x=5, y=3, z;
z = addition ( x, y );

Arguments passed by
reference
 Passing by reference refers to a method of passing
arguments where the value of an argument in the
calling function can be modified in the called
function.
 It allows to access an external variable from within
a function

passing parameters by reference
#include <iostream>
using namespace std;
void duplicate (int& a, int& b, int& c) {
a*=2;
b*=2;
c*=2;
}
int main () {
int x=1, y=3, z=7;
duplicate (x, y, z);
cout << "x=" << x << ", y=" << y << ", z=" << z;
return 0;
}

Explanation
 When a variable is passed by reference, what is passed is no
longer a copy
 the variable itself, identified by the function parameter
associated with the argument passed to the function
 any modification on local variables within the function are
reflected in the variables passed as arguments in the call

Declaration
 If instead of defining duplicate as:
 void duplicate (int& a, int& b, int& c)
 Was it to be defined without the ampersand signs as:
void duplicate (int a, int b, int c)
 The variables would not be passed by reference, but by
value, creating instead copies of their values.
 In this case, the output of the program would have
been the values of x, y, and z without being modified
(i.e., 1, 3, and 7)

Recursive Functions
 Recursive is the property that functions have to be
called by themselves
 n! = n * (n-1) * (n-2) * (n-3) ... * 1
 5! = 5 * 4 * 3 * 2 * 1 = 120
while ( i <= number) {
Factorial = Factorial * i;
++i;
}

Recursive Function
int factorial (int a) {
if (a > 1)
return (a * factorial (a-1));
else
return 1;
}

C++ Standard Library
 Refer the following website and find the C++ standard
header files and inbuilt functions.
 www.cplusplus.com/reference/

C++ lecture 03

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