C++ ProgrammingLecture 13

Functions – Part V

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Department

(Adapted from the textbook slides)

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Outline Introduction. Functions with empty parameter lists. Inline functions. Functions with default arguments. Functions overloading. Functions templates. Examples.

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Functions with Empty Parameter Lists

Empty parameter lists Either writing void or leaving a parameter list empty

indicates that the function takes no argumentsvoid print(); or void print( void );

Function print takes no arguments and returns no value Calling a function that does not return any value inside

cout statement is syntax error (cout<<print() syntax error)

Passing parameter to a function that does not take any parameter is syntax error (print (5), or print (x) syntax error)

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1 // Fig. 3.18: fig03_18.cpp2 // Functions that take no arguments3 #include <iostream>45 using std::cout;6 using std::endl;78 void function1();9 void function2( void );1011 int main()12 {13 function1();14 function2();1516 return 0;17 }1819 void function1()20 {21 cout << "function1 takes no arguments" << endl;22 }2324 void function2( void )25 {26 cout << "function2 also takes no arguments" << endl;27 }

function1 takes no argumentsfunction2 also takes no arguments

Notice the two ways of declaring no arguments.

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Inline Functions inline functions

Reduce function-call overhead Asks the compiler to copy code into program

instead of using a function call Compiler can ignore inline Should be used with small, often-used functions

Example:inline double cube( const double s )

{ return s * s * s; }

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Default Arguments I In the function prototype give all or some of the

arguments default values. When you call the function, you can omit one or

more of the arguments values. The omitted arguments will take their values from the default values in the function prototype.

If function parameter omitted, gets default value Can be constants, global variables, or function calls If not enough parameters specified (in the calling

statement), rightmost go to their defaults Default arguments in the prototype must be the right

most arguments or parameters for a function. Can be used with inline functions also.

Set defaults in function prototype (only) where the variables names are provided just for readability.int defaultFunction( int x = 1, int y = 2, int z = 3 );

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Default Arguments II In a function call you can omit the

parameters that have default values only.

Not setting all the rightmost parameters after a default arguments to default is a syntax error.

E.g.:int defaultFunction(int x = 1, int y, int z = 3); Syntax errorint defaultFunction( int x = 1, int y, int z); Syntax errorThis means that no argument can take a default value unless the one on its right has a default value

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1 // Fig. 3.23: fig03_23.cpp2 // Using default arguments3 #include <iostream>45 using std::cout;6 using std::endl;78 int boxVolume( int length = 1, int width = 1, int height = 1 );910 int main()11 {12 cout << "The default box volume is: " << boxVolume() 13 << "\n\nThe volume of a box with length 10,\n"14 << "width 1 and height 1 is: " << boxVolume( 10 ) 15 << "\n\nThe volume of a box with length 10,\n" 16 << "width 5 and height 1 is: " << boxVolume( 10, 5 )17 << "\n\nThe volume of a box with length 10,\n"18 << "width 5 and height 2 is: " << boxVolume( 10, 5, 2 )19 << endl;2021 return 0;22 }2324 // Calculate the volume of a box 25 int boxVolume( int length, int width, int height )26 { 27 return length * width * height;28 }

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Program Output

The default box volume is: 1 The volume of a box with length 10,width 1 and height 1 is: 10 The volume of a box with length 10,width 5 and height 1 is: 50 The volume of a box with length 10,width 5 and height 2 is: 100

Notice how the rightmost values are defaulted.

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Function Overloading I Function overloading means having functions with

same name and different parameters (different number of parameters, or different data types, or different order, or all of these issues at the same time)

Goal: having functions with the same name but they do different tasks

Most of the time overloaded functions perform similar tasks ( i.e., a function to square ints, and function to square floats).

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

Program chooses function by signature signature is determined by function name and its

parameters Can have the same return types

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Function Overloading II You cannot overload a function with default

arguments with another version that takes no arguments syntax error.

Overloading a function with another version that have the same parameters numbers, types, and order with just the return result data type is different is a syntax error.

Operator overloading like >> and <<, also & will be taken in OOP course.

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Function overloading III#include<iostream>using namespace std;

int fun1(int ,float ,char );int fun1(int , float, char);

int main(){

cout<<(5,3.3,'a');

return 0;}

int fun1(int x1,float y1,char z1)

{return x1+y1+z1;}

int fun1(int x,float y,char z){return x+y+z;}

#include<iostream>using namespace std;

int fun1(int ,float ,char );float fun1(int , float, char);

int main(){

cout<<(5,3.3,'a');

return 0;}

int fun1(int x1,float y1,char z1)

{return x1+y1+z1;}

float fun1(int x,float y,char z){return x+y+z;}

#include<iostream>using namespace std;

int fun1(int ,float ,char );int fun1(float, int , char);

int main(){

cout<<(5,3.3,'a');

return 0;}

int fun1(int x1,float y1,char z1)

{return x1+y1+z1;}

int fun1(float y, int x,char z){return x+y+z;}

#include<iostream>using namespace std;

int fun1(int ,float ,char );int fun1(int , float);

int main(){

cout<<(5,3.3,'a');

return 0;}

int fun1(int x1,float y1,char z1)

{return x1+y1+z1;}

int fun1(int x,float y){return x+y+z;}

Syntax error. Two functions are the same

Syntax error. changing return type is not enough

Parameters order is different so it is ok

# of parameters is different so it is ok

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1 // Fig. 3.25: fig03_25.cpp2 // Using overloaded functions3 #include <iostream>45 using std::cout;6 using std::endl;78 int square( int x ) { return x * x; }910 double square( double y ) { return y * y; }1112 int main()13 {14 cout << "The square of integer 7 is " << square( 7 )15 << "\nThe square of double 7.5 is " << square( 7.5 ) 16 << endl; 1718 return 0;19 }

The square of integer 7 is 49The square of double 7.5 is 56.25

Functions have same name but different parameters

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Function Templates I Function templates

Used only when the overloaded functions have the same logic (body) and same number of parameters (just the data type is different)

Compact way to make overloaded functions Keyword template Keyword class or typename before every

formal type parameter (built in or user defined)

template < class T > // or template< typename T >T square( T value1 ){ return value1 * value1;}

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Function Templates II T replaced by type parameter in function call.

int x;int y = square(x);

If int, all T's become ints Can use float, double, long...

You can use any character to replace T, e.g. class R.

You can specify the return data type for a template function (not always put it as T).

You can specify the data type of some parameters (not always put it as T).

Passing different values for T is syntax error.

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Example// Fig. 3.27: fig03_27.cpp, Using a function template.#include <iostream>

using namespace std;

// definition of function template maximumtemplate < class T > // or template< typename T >T maximum( T value1, T value2, T value3 ){ T max = value1;

if ( value2 > max ) max = value2;

if ( value3 > max ) max = value3;

return max;

} // end function template maximum

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Example … cont.int main(){ // demonstrate maximum with int values int int1, int2, int3;

cout << "Input three integer values: "; cin >> int1 >> int2 >> int3;

// invoke int version of maximum cout << "The maximum integer value is: “ << maximum( int1, int2, int3 );

// demonstrate maximum with double values double double1, double2, double3;

cout << "\n\nInput three double values: "; cin >> double1 >> double2 >> double3;

// invoke double version of maximum cout << "The maximum double value is: “ << maximum( double1, double2,

double3 );

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Example … cont.// demonstrate maximum with char values char char1, char2, char3;

cout << "\n\nInput three characters: "; cin >> char1 >> char2 >> char3;

// invoke char version of maximum cout << "The maximum character value is: " << maximum( char1, char2, char3 ) << endl;

return 0; // indicates successful termination

} // end main

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Output for the previous code

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Additional Notes This lecture covers the following

material from the textbook: Fourth Edition

Chapter 3: Sections 3.15, 3.16, 3.18, 3.20, 3.21