CS1201:
Programming Language 2
By:Nouf Aljaffan
Edited by : Nouf Almunyif
Function I
Global VS Local variables
• local variable
▫ Variables that declared inside a function
▫ Declared inside any block of code
• Global variables
▫ Opposite of local the known throughout the entire
program
Global VS Local variables
#include < iostream>
Using namespace std;
Global VS Local variables
I is 5
I is 100
I is 5
#include < iostream>
Using namespace std;
void main() {
int i=4; int j=10;
i++;
if (j > 0)
cout<<“ i is “<<i<<endl;
if (j > 0)
{ int i=100;
/* 'i' is defined and so local to * this block */
Cout << "i is” << i;
} //end if
cout<<"i is “<<i;
} //end main
Function
• The function are reusable.
• functions may be called Procedures or Routines and
in object oriented programming called Methods .
• Save programmers’ time.
Prototype VS. Declaration
prototype : normally placed before the start of main()
but must be before the function definition.
General form :
function_return_type function_name (type
parameter1, type parameter2,…, type parameterN) ;
EX:
void Factorial (int x); // prototype -- x is a parameter
Prototype VS. Declaration
Prototype :
void foo(int x); // prototype -- x is a parameter
• Declaration
• void foo(int x) // declaration -- x is a parameter
{
Statement
.
.
.
}
EX:
#include<iostream>
using namespace std;
int square (int x)
{
return x*x;
}
Void main ( )
{
int number;
cout<<"Enter any number to Calculate the square of this number ";
cin>>number;
cout<<endl;
cout<<"the square of "<<number<<" is " <<square(number)<<endl;
}
EX:
#include<iostream>
using namespace std;
int square (int x) ;
Void main ( )
{
int number;
cout<<"Enter any number to Calculate the square of this number ";
cin>>number;
cout<<endl;
cout<<"the square of "<<number<<" is " <<square(number)<<endl;
}
int square (int x)
{ return x*x; }
Finding Errors in Function Code
int sum(int x, int y)
{
int result;
result = x+y;
}
this function must return an integer value as
indicated in the header definition
(return result;) should be added
Finding Errors in Function Code
int sum (int n)
{ if (n==0)
return 0;
else
n+(n-1);
}
the result of n+sum(n-1) is not returned;
sum returns an improper result, the else part
should be written as:else return n+(n-1);
Finding Errors in Function Code
void f(float a);
{
float a;
cout<<a<<endl;
}
; found after function definition header.
 redefining the parameter a in the function
void f(float a)
{
float a2 = a + 8.9;
cout <<a2<<endl;
}
Finding Errors in Function Code
void product(void)
{
int a, b, c, result;
cout << “enter three integers:”;
cin >> a >> b >> c;
result = a*b*c;
cout << “Result is” << result;
return result;
}
According to the definition it should
not return a value , but in the block
(body) it did & this is WRONG.
 Remove return Result;
Parameters vs Arguments
• Up until now, we have not differentiated between
function parameters and arguments.
• In common usage, the terms parameter and argument
are often interchanged.
▫ A function parameter is a variable declared in the
prototype or declaration of
▫ An argument is the value that is passed to the
function in place of a parameter.
methods of passing
• There are 2 primary methods of passing
arguments to functions:
▫ pass by value,
▫ pass by reference,
Passing arguments by value
• By default, arguments in C++
are passed by value.
• When arguments are passed
by value, a copy of the
argument is passed to the
function.
void foo(int y)
{
cout << "y = " << y << endl;
}
int main()
{
foo(5); // first call
int x = 6;
foo(x); // second call
foo(x+1); // third call
return 0;
}
Passing arguments by value
• Because a copy of the
argument is passed to
the function, the
original argument
can not be modified
by the function.
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void foo(int y)
{
cout << "y = " << y << endl;
y = 6;
cout << "y = " << y << endl;
} // y is destroyed here
int main()
{
using namespace std;
int x = 5;
cout << "x = " << x << endl;
foo(x);
cout << "x = " << x << endl;
return 0;
}
Adv. And DisAdv. Of Passing by value
Advantages
▫ Arguments passed by value
can be:
 variables (eg. x),
 literals (eg. 6),
 or expressions (eg. x+1) or
(eg foo()).
▫ Arguments are never
changed by the function
being called, which prevents
side effects.
Disadvantages

Copying large structs or
classes can take a lot of time to
copy, and this can cause a
performance penalty,
especially if the function is
called many times.