Inbuilt Functions in C++ computer language.ppt

Introduction
 Using functions we can structure our
programs in a more modular way, accessing
all the potential that structured programming
can offer to us in C++
 A function is a group of statements that is
executed when it is called from some point of
the program.

Functions
 In C++, functions are characterized by a name, a
return type and by a list of arguments (optional)
 The argument list must always be present (even in
the case it is empty)
 The return value must be compatible (maybe by
means of an explicit cast) with the function type
return value
double max( double a, double b)
{
return (a>b) ? a : b;
}
return type arguments
function body

Function prototypes
 A function must be declared before you can use it (in the file
where it is used)
 Function prototypes make C++ functions “type safe”, the
compiler can always convert the real values of the
arguments to the types formally specified in the prototype
#include <iostream>
double max(double, double);
int main()
{
double m = max(1, 3);
cout<<“the maximum is “<<m<<endl;
return 0;
}
main.cpp
double max (double a, double b)
{
return (a>b) ? a : b;
}
max.cpp
max prototype
(usually in max.h)

Exercise
 Write a C++ program that will ask for a temperature in
Fahrenheit and display in Celsius.
#include<iostream.h>
float ftoc(float f){
float c;
c = float((f-32.0) * 5/9);
return c;
}

Exercise
int main(){
float farTemp,celTemp;
float ftoc(float farTemp);
cout<<"Enter the temperature in Fahrenheit : ";
cin>>farTemp;
cout<<"n";
celTemp = ftoc(farTemp);
cout<<"Equivalent in Celcius is: ";
cout << celTemp<<"nn";
return 0;
}

Call by Reference
 Use of references allows a function to modify the value of its
arguments
 The reference can be defined const so that the function can
not modify that argument
bool greater(int& i, int& j) {
if (i>j) {
int temp=i;
i=j;
j=temp;
return true;
}
else
return false;
}
Arguments passed “by reference”
The function can modify its
arguments

Default Arguments
 A default value can be assigned to all arguments of a
function. The function can then be called by omitting those
parameter for which a default value has been specified
 A default value can only be specified for the rightmost
parameters in the calling sequence
int pow(int , int);
int main()
{
int r=3;
int a1=pow(3,3); // a1=27
int a2=pow(3); // a2=9
return 0;
}
main.cpp
int pow (int a, int k=2)
{
if (k==2) return a*a;
else return a*pow(a, k-1);
}
pow.cpp
Default argument

#include <iostream>
using namespace std;
int AreaCube(int length, int width = 25, int height = 1);
int main()
{
int length = 100;
int width = 50;
int height = 2;
int area;
area = AreaCube(length, width, height);
cout << "First area equals: " << area << "n";
area = AreaCube(length, width);
cout << "Second time area equals: " << area << "n";
area = AreaCube(length);
cout << "Third time area equals: " << area << "n";
return 0;
}
int AreaCube(int length, int width, int height)
{
return (length * width * height);
}

inline functions
 The inline keyword is used to suggest the compiler
that all calls to that function must be replaced with
executable code (all calls are replaced with the
function’s definition, everywhere in the code)
 inline functions are used for efficiency reasons and
must be kept simple (not to get the compiler
overworked)
 The compiler will decide autonomously (for
instance if the function is too big) whether to
ignore the inline directive or not

#include <iostream>
using namespace std;
inline int Double(int);
int main()
{
int target;
cout << "Enter a number to work with: ";
cin >> target; 13: cout << "n";
target = Double(target);
cout << "Target: " << target << endl;
return 0;
}
int Double(int target)
{
return 2*target;
}

Overloading
 Different functions can carry the same name
 The function being called is then chosen by the compiler on
the basis of the return type and on the argument number
and type
double average_array(const int a[], int size)
{
int sum=0;
for (int i=0;i<size;i++) sum+=a[i];
return double(sum)/size;
}
double average_array(const double a[], int size)
{
double sum=0;
for (int i=0;i<size;i++) sum+=a[i];
return sum/size;
}
average_array.cpp

Overloading
 The list of arguments and their types is called the function’s
signature
 The return type is not part of a function’s signature, the number
and the ordering of the arguments is on the other hand crucial
void print(int i=0) {. . .} // (1)
void print(int i, double x) {. . .} // (2)
void print(double y, int i) {. . .} // (3)
. . .
print(‘A’); // ‘A’ is converted to int, (1) is called
print(str[]); // error! No conversion is possible
print(15,9); // error! Ambiguity between (2) and (3)
print(15,9.); // OK, (2) is called
print(); // OK, (1) is called (default argument)

The main() arguments
 By specifying a list of arguments for main() it is possible to have
access to all parameters passed on the command line:
 argc is the # of parameters passed on the command line (at least
1, the program name) argv contains all single parameters
#include <iostream.h>
int main(int argc, char *argv[])
{
cout<<“ argc value: “<<argc<<endl;
cout<<“ the executable name is “<<*argv<<endl;
for (int i=1; i<argc; i++)
cout<<“Arg #”<<i<<“ = “<<*(argv+i)<<endl;
return 0;
}

The main() arguments (2)
 If you run this program with the following
command
prompt> mytest this is a test
 ..you’ll get
argc value : 5
the executable name is e` mytest
Arg #1 = this
Arg #2 = is
Arg #3 = a
Arg #4 = test

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