CSC1201: Programming Language 2 1 Functions. 2 Function declaration: return_type FuncName( Type arg1, Type arg2,….. Type argN) { function body } A program

$Page 1: CSC1201: Programming Language 2 1 Functions. 2 Function declaration: return_type FuncName( Type arg1, Type arg2,….. Type argN) { function body } A program$
CSC1201: Programming Language 2

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Functions

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Function declaration:return_type FuncName(Type arg1, Type arg2,….. Type argN)

{ function body }• A program can contain one or many functions• Must always have a function called “main”.• The main function is the starting point of all C++ programs• The compiler will not compile the code unless it finds a function called

“main” within the program.

A Function is a group of statements that together perform a task.It can be used anywhere in the program. Why we need function? – Organize code in program– Code are easier to maintain?

“Hello World” program

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#include <iostream>using namespace std;int main (){cout << “Hello World\n”;Return 0;}

Function

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When we need function?– When you need to repeat the same process over and over in a program.– The function can be called many times but appears in the code once.

1- Predefined functions

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Predefined functions are functions that are built into C++ Language to perform some standard operations.

The C++ standard library provides numerous built-in functions that your program can call. For example, function strcat() to concatenate two strings

the definitions have been written and it is ready to be used.

User needs to include pre-defined header file (i.e. math.h, time.h)

2- User defined functions

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Function that been created by the user.

This functions need to be declared and defined by the

user

functions

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Value returning functions: functions that have a return type. These functions return a value of a specific data type using

the return statement.

Void functions: functions that do not have a return type. These functions do not use a return statement to return a

value.

Value returning functions

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The syntax is:

FuncType FuncName(formal parameter list ){

statements}

Void functions

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The syntax is:Void FuncName ( formal parameter list ){

statements}

Examples:

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1. Write a Function larger, which returns the larger of the two given doubles.

2. Write a Function Square, which returns the square of the given integer.

3. Write a function number_type. The function should output the number and message saying whether the number is positive, negative, or zero.

Example: With return value

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#include<iostream>using namespace std;

Double larger ( double x , double y ){

double max;

if ( x >= y )max = x;

elsemax = y;

return max;}int main ( ){cout << “The larger of 5 and 6 is “ << larger(5 , 6) << endl; //Function Callreturn 0;}

Example: With return value

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#include<iostream>using std::cin;using std::cout;using std::endl;

int square (int x){

return x*x;}

int 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; //Function Callreturn 0;

}

Example: Without return value

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void number_type ( int x){

if ( x > 0 )cout << x << “ is positive.” << endl;

else if ( x < 0 )cout << x << “ is negative.” << endl;

elsecout<< x << “is a zero.”<<endl;

}int main ( ){number_type( 5 ); //Function Callreturn 0;}

Function

The function are reusablereusable. Functions may be called ProceduresProcedures or RoutinesRoutines and in

object oriented programming called MethodsMethods . Save programmers’ time.

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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

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Prototype VS. Declaration

Prototype :void foo(int x); // prototype -- x is a parameter

Declaration void foo(int x) // declaration -- x is a parameter{Statements...}

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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;

}17

EX:


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; }18

Finding Errors in Function Codeint 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

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Finding Errors in Function Codeint sum (int n){ if (n==0)

return 0;else

n+(n-1);}

the result of n+(n-1) is not returned; sum returns an improper result, the else

part should be written as -:else return n+(n-1);

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Finding Errors in Function Codevoid 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;

}21

Finding Errors in Function Codevoid 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;

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Scope of variables

C++ Variables A variable is a place in memory that has

A name or identifier (e.g. income, taxes, etc.) A data type (e.g. int, double, char, etc.) A size (number of bytes) A scope (the part of the program code that can

use it) Global variables – all functions can see it and using it Local variables – only the function that declare local

variables see and use these variables A life time (the duration of its existence)

Global variables can live as long as the program is executed

Local variables are lived only when the functions that define these variables are executed

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Global VS Local variablesGlobal VS Local variables

local variable Variables that declared inside a function

Declared inside any block of code

Global variablesOpposite of local the known throughout the entire program

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#include < iostream>Using namespace std;

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#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

I is 5I is 100I is 5

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Scope of Local Variables, cont.

void function1() { int x = 1; int y = 1;

for (int i = 1; i < 10; i++) {

x += i; }

for (int i = 1; i < 10; i++) {

y += i; } }

It is fine to declare i in two non-nesting blocks

void function2() { int i = 1; int sum = 0;

for (int i = 1; i < 10; i++) { sum += i; } cout << i << endl; cout << sum << endl;

}

It is not good practice to declare i in two nesting blocks

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Variable Scope

In fact, you can reuse names in a scope which is nested inside another scope

int main ( ) { int i = 5, j = 0;

for (j = 0; j < 10; j++) { int i = j; // OK, this is new i int k = 5; doSomething (i); } int sum = k; // compile error, no k in scope j = i; // sets j to 5 for (j = 0; j < 100; j++ ) { int i = j; // yet another new i } int i = 0; // compile error –redefined variable}void doSomething(int i){ cout<<++i;}// OK, this is new i

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Variable Scope Local variables of same name can be nested inside

global variables

int total = 5;

int main ( ) { int total = 4; // OK, this is nested scope ….}int sub1 ( ) { int i = total; // OK, i set to 5}

#include<iostream>using namespace std;int i = 10;int main ( ) { cout<<i<<endl;//10 for (int j = 0; j < 10; j++ ) {

int i = 20; cout<<i<<endl;//20

}cout<<i<<endl;//10 int i = 30;cout<<i<<endl;//30cout<<i<<endl;//30return 0;}

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I. Using Global Variables#include <iostream>using namespace std;

int x = 0;void f1() { x++; }void f2() { x+=4; f1(); }void main(){ f2(); cout << x << endl;}

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I. Using Global Variables#include <iostream>using namespace std;int x = 0;void f1() { x++; }void f2() { x+=4;

f1(); }void main(){ f2(); cout << x << endl;}

x 0

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x 0

void main()void main(){ { f2();f2(); cout << x << endl ;cout << x << endl ;}}

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x 0


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void f2()void f2(){ { x += 4;x += 4; f1();f1();}}

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4

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x


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void f2()void f2(){ { x += 4;x += 4; f1();f1();}}

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void f1()void f1(){ { x++;x++;}}

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x

void main()void main(){ { f2();f2(); cout << x << endl;cout << x << endl;}}

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void f2()void f2(){ { x += 4;x += 4; f1();f1();}}

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void f1()void f1(){ { x++;x++;}}5

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x


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void f2()void f2(){ { x += 4;x += 4; f1();f1();}}6

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x


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void main()void main(){ { f2();f2(); cout << x << endl;cout << x << endl;}}8

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What is Bad About UsingGlobal Vairables?

Not safe! If two or more programmers are working

together in a program, one of them may change the value stored in the global variable without telling the others who may depend in their calculation on the old stored value!

Against The Principle of Information Hiding! Exposing the global variables to all functions is

against the principle of information hiding since this gives all functions the freedom to change the values stored in the global variables at any time (unsafe!)

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Local Variables Local variables are declared inside the

function body and exist as long as the function is running and destroyed when the function exit

You have to initialize the local variable before using it

If a function defines a local variable and there was a global variable with the same name, the function uses its local variable instead of using the global variable

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Example of Defining and Using Global and Local Variables

#include <iostream>using namespace std;int x; // Global variable// Global variableVoid fun(); // function // function

prototypeprototypevoid main(){ x = 4; fun(); cout << x << endl;} void fun(){ int x = 10; // Local variable// Local variable cout << x << endl;}

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#include <iostream>using namespace std;int x; // Global variable// Global variableVoid fun(); // function prototype// function prototype

void main(){ x = 4; fun(); cout << x << endl;}

void fun(){ int x = 10; // Local variable// Local variable cout << x << endl;}

x 0

Global variables are automatically initialized to 0

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void main(){ x = 4; fun(); cout << x << endl;} void fun(){ int x = 10; // Local variable// Local variable cout << x << endl;}

x 0

void main()void main(){ { x = 4;x = 4; fun();fun(); cout << x << endl;cout << x << endl;}}

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x 4


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void fun()void fun()

{ { int x = 10;int x = 10; cout << x << endl;cout << x << endl;}}

x ????

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x 4


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x 10

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x 4


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x 10

4

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#include <iostream>using namespace std;

int x; // Global variable// Global variableVoid fun(); // function signature// function signature



x 4


2



x 10

5

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Example of Defining and Using Global and Local Variables#include <iostream>using namespace std;int x; // Global variable// Global variableVoid fun(); // function prototype// function prototype



x 4


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Example of Defining and Using Global and Local Variables#include <iostream>using namespace std;int x; // Global variable// Global variableVoid fun(); // function prototype// function prototype



x 4

void main()void main(){ { x = 4;x = 4; fun();fun(); cout << x << endl;cout << x << endl;}}752

Example of Using Value Parameters and Global Variables#include <iostream>using namespace std;int x; // Global variable// Global variablevoid fun(int x){ cout << x << endl;

x=x+5;}void main(){ x = 4; fun(x/2+1); cout << x << endl;}

x 0

void main()void main(){ { x = 4;x = 4; fun(x/2+1);fun(x/2+1); cout << x << endl;cout << x << endl;}}

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x 4


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void fun(int x )void fun(int x ){ { cout << x << endl;cout << x << endl; x=x+5;x=x+5;}}

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x 4


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3

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x 4


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x 4


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x 4

void main()void main(){ { x = 4;x = 4; fun(x/2+1);fun(x/2+1); cout << x << endl;cout << x << endl;}}758

Methods of Passing

Methods of Passing There are 2 primary methods of passing

arguments to functions: pass by value, pass by reference,

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Absolute value#include <iostream>using namespace std;int absolute (int);// function prototype for absolute()int main(){ int num, answer; cout << "Enter an integer (0 to stop): "; cin >> num;

while (num!=0){ answer = absolute(num); cout << "The absolute value of " << num << " is: " << answer << endl; cin >> num; }

return 0; } // Define a function to take absolute value of an integer int absolute(int x){ if (x >= 0) return x; else return -x; }

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Methods of Passing There are 2 primary methods of passing

arguments to functions: pass by value, pass by reference,

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Passing arguments by reference When passing arguments by value, the only way to return

a value back to the caller is via the function’s return value.

While this is suitable in many cases, there are a few cases where better options are available.

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Passing arguments by reference

In pass by reference, we declare the function parameters as references rather than normal variables:

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void AddOne(int &y) // y is a reference variable{ y = y + 1;}

• When the function is called, y will become a reference to the argument.

• The reference to a variable is treated exactly the same as the variable itself.

• any changes made to the reference are passed through to the argument!

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Sometimes we need a function to return multiple values.

However, functions can only have one return value. One way to return multiple values is using reference

parameters

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Cont. Example

void foo(int &y) // y is now a reference{ cout << "y = " << y << endl; y = 6; cout << "y = " << y << endl;} // y is destroyed here int main(){ int x = 5; cout << "x = " << x << endl; foo(x); cout << "x = " << x << endl; return 0;}

This program is the same as the one we used for the pass by value example, except foo’s parameter is now a reference instead of a normal variable.

When we call foo(x), y becomes a reference to x.

Note that the value of x was changed by the function!

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Example 2void AddOne(int &y){ y++;} int main(){ int x = 1; cout << "x = " << x << endl; AddOne(x); cout << "x = " << x << endl; return 0;}

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Example 3#include <iostream>Using namespace std ;Void duplicate (int& a, int& b, int & c); Void main (){ Int x=1,y=3,z=7;

Duplicate (x,y,z);Cout << “x=“<<x<<“, y=“<<y<<“,z=“<<z;

}

Void duplicate (int& a, int& b, int & c){ a*=2;

b*=2;c*=2;

}

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Example 4#include <iostream>Using namespace std ;void swap(float &x, float &y); int main() {

float a, b; cout << "Enter 2 numbers: " << endl; cin >> a >> b;

if(a>b) swap(a,b); cout << "Sorted numbers: "; cout << a <<

" " << b << endl; return 0; } void swap(float &x, float &y) { float temp; temp = x; x = y; y = temp; }

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#include <iostream>#include <math.h> // for sin() and cos()Using namespace std; void GetSinCos(double dX, double &dSin, double &dCos){ dSin = sin(dX); dCos = cos(dX);} int main(){ double dSin = 0.0; double dCos = 0.0; GetSinCos(30.0, dSin, dCos); cout << "The sin is " << dSin << endl; cout << "The cos is " << dCos << endl; return 0;}

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Advantages of passing by reference It allows us to have the function change the value of the

argument, which is sometimes useful. Because a copy of the argument is not made, it is fast, even

when used with large structus or classes. We can pass by CONST reference to avoid unintentional

changes. We can return multiple values from a function.

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Function Overloading

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Function Overloading Two or more functions can have the same

name but different parameters Example:

int max(int a, int b) {if (a>= b)

return a;else

return b;}

float max(float a, float b) {if (a>= b)

return a;else

return b;}

Function Overloading In a C++ program, several functions can have

the same name This is called function overloading or

overloading a function name

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Function Overloading (continued) Two functions are said to have different

formal parameter lists if both functions have: A different number of formal parameters, or If the number of formal parameters is the same,

then the data type of the formal parameters, in the order you list them, must differ in at least one position

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The functions functionSix and functionSeven both have three formal parameters and the data type of the corresponding parameters is the same; therefore, these functions have the same formal parameter list

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• Function overloading: creating several functions with the same name

• The signature of a function consists of the function name and its formal parameter list

• Two functions have different signatures if they have either different names or different formal parameter lists

• Note that the signature of a function does not include the return type of the function

Function Overloading (continued)

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These function headings correctly overload the function functionXYZ:

• Both of these function headings have the same name and same formal parameter list

• Therefore, these function headings to overload the function functionABC are incorrect

• In this case, the compiler will generate a syntax error

• Note that the return types of these function headings are different

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Functions with Default Parameters When a function is called

The number of actual and formal parameters must be the same

C++ relaxes this condition for functions with default parameters

You specify the value of a default parameter when the function name appears for the first time, such as in the prototype

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Functions with Default Parameters (continued)

If you do not specify the value of a default parameter The default value is used

All of the default parameters must be the rightmost parameters of the function

In a function call where the function has more than one default parameter and a value to a default parameter is not specified You must omit all of the arguments to its right

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Functions with Default Parameters (continued)

Default values can be constants, global variables, or function calls

The caller has the option of specifying a value other than the default for any default parameter

You cannot assign a constant value as a default value to a reference parameter

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Function Overloading Function overloading

Functions with same name and different parameters or return data type

Should perform similar tasks I.e., function to square ints and function to square floats

int square( int x) {return x * x;}float square(float x) { return x * x; }

A call-time c++ complier selects the proper function by examining the number, type and order of the parameters

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Function overloadingExample

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#include <iostream>using namespace std;

void FtoC(int temp);void FtoC(float temp);void FtoC(double temp);

int main(){ int inttemp, level; float floattemp; double doubletemp;cout << "CONVERTING FAHRENHEIT TO CELSIUS\n"; cout << "Select required level of precision\n"; cout << "Integer (1) - Float (2) - Double (3)\n"; cin >> level;

cout << "Enter Fahrenheit temperature: ";switch (level) { case 1 : cin >> inttemp;

FtoC(inttemp); break;

case 2 : cin >> floattemp; FtoC(floattemp); break;

case 3 : cin >> doubletemp; FtoC(doubletemp);break;

default : cout << "Invalid selection\n"; } return 0;}

Function overloading

Cont .

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void FtoC( int itemp)} int temp = (itemp - 32) * 5 / 9; cout << "Integer precision" :; cout << itemp << "F is " << temp << "C\n";{

void FtoC( float ftemp)} float temp = (ftemp - 32) * 5.0 / 9.0; cout << "Float precision" :; cout << ftemp << "F is " << temp << "C\n";;{

void FtoC( double dtemp)

}

double temp = (dtemp - 32) * 5.0 / 9.0;

cout << "Double precision" : ;

cout << dtemp << "F is " << temp << "C\n";;

{

By: Nouf Almunyif

Recursion

Recursion and Recursive Functions Main calls another function…..normal A function calls another function2….normal A function calls itself ?! Possible??

YESA recursive function is one that call itself.

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General form void recurse(){ recurse(); //Function calls itself}

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Finding Factorial 5! = 5*4*3*2*1

5!

5*4!

4*3!

3*2!

2*1!

1

5!

5*4!

4*3!

3*2!

2*1!

1

Final value=120

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2!=2*1=2 returned

3!=3*2=6 returned

4!=4*6=24 returned

5!=5*24=120 returned

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Finding Factorial #incloud <iostream>; Using nampespace std; Void main() { int n,factorial,i; cout << "Enter a positive integer: "; cin >> n; for (i = 1; i <= n; i++)

{ if (i == 1) factorial = 1; Else factorial = factorial * i; }

cout << "The factorial of " << n << " is " << factorial << endl;

}91

Finding Factorial Recursively//Recursive factorial Function#include<iostream>

Int factorial(int N);Void main(){ int num;

cout<<“Enter a positive integer:”;cin>>num;cout<<“factorial=“<<factorial(num);

}Int factorial( int N){

if ( N <= 1) //the base casereturn 1;

elsereturn N * factorial (N - 1);

}

N=4Retrun 4

*factorial(3)N=3

Retrun 3 *factorial(2)

N=2Retrun 2

*factorial(1)

N=1Retrun 1

Enter a positive integer : 4

12*1 = 2

23*2 =6

64*6=24

Factorial = 24

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Example printing number counting down

#include <iostream>using namespace std; void myMethod( int counter){if(counter == 0) return; // no value returning just for EXIT

the functionelse { cout<<counter<<endl; myMethod(--counter); return; // no value returning just for EXIT

the function }}

void main(){

int input;cout<<"enter positive number ";cin>>input;myMethod(input);

}

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Documents

CSC1201: Programming Language 2 1 Functions. 2 Function declaration: return_type FuncName( Type arg1, Type arg2,….. Type argN) { function body } A program