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MODULE 4b
MORE ON C/C++ FUNCTIONS - PROGRAM EXAMPLES 3
Receive nothing, return nothing-receive nothing, return something-
receive something, return something-receive something, return nothing
And they do something. That is a function!
My Training Period: xx hours
This is a continuation from the previous Module. The source code for this Module is: C/C++ functions source codes and the lab worksheets for your practice: Function lab worksheet 1, lab worksheet 2, lab worksheet 3 and lab worksheet 4.
C and C++ abilities
▪ Able to understand function program examples and do the function programming.
▪ Able to appreciate the recursive function.
▪ Able to find predefined/built-in standard and non-standard functions resources.
▪ Able to understand and use predefined/built-in standard and non-standard functions.
▪ Able to understand and use the variadic functions.
Program Examples and Experiments
Example #1
// function skeleton example, passing by values
#include <iostream>
using namespace std;
// function prototypes and their variations...
// notice and remember these variations...
void FunctOne(void);
double FunctTwo();
int FunctThree(int);
void FunctFour(int);
// main program...
void main()
{
cout<<"I'm in main()..."<<endl;
// function call, go to FunctOne without any argument...
FunctOne();
cout<<"\nBack in main()..."<<endl;
// function call, go to FunctTwo without any argument...
double q = FunctTwo();
// display the returned value...
cout<<"The returned value = "<<q<<endl;
// function call, go to FunctThree with an argument...
int y = 100;
int x = FunctThree(y);
cout<<"Back in main()..."<<endl;
// display the returned value...
cout<<"Display the returned value = "<<x<<endl;
int r = 50;
FunctFour(r);
// return nothing or just omit this 'return;' statement
return;
}
void FunctOne()
{
// do nothing here just display the following text...
cout<<"\nNow I'm in FunctOne()!..."<<endl;
cout<<"Receives nothing, return nothing..."<<endl;
// return to main, without any returned value
// return; optionally can put this empty 'return;'
}
double FunctTwo()
{
// receive nothing but do some work here...
double p = 10.123;
cout<<"\nNow I'm in FunctTwo()!\nmay do some work here..."
<<"\nReceives nothing but return something"
<<"\nto the calling function..."<<endl;
// and return something...
return p;
}
int FunctThree(int z)
{
// receive something...do some work and return the something...
int a = z + 100;
cout<<"\nThen, in FunctThree()!..."<<endl;
cout<<"Receive something from calling function\ndo some work here and"
<<"\nreturn something to the calling function...\n"<<endl;
// then return to main, with return value
return a;
}
void FunctFour(int s)
{
// received something but return nothing...
int r = s - 20;
cout<<"\nNow, in FunctFour()..."<<endl;
cout<<"Received something, but return nothing..."<<endl;
cout<<"The value processed = "<<r<<endl;
// return; optionally can put this empty 'return;'
}
Output:
Example #2
// demonstrates the use of function prototypes
#include <iostream>
using namespace std;
// another method simplifying type identifier using typedef
// the words unsigned short is simplified to USHORT
typedef unsigned short USHORT;
// a function prototype
USHORT FindTheArea(USHORT length, USHORT width);
int main()
{
USHORT lengthOfYard;
USHORT widthOfYard;
USHORT areaOfYard;
cout<< "\nThe wide of your yard(meter)? ";
cin>> widthOfYard;
cout<< "\nThe long of your yard(meter)? ";
cin>> lengthOfYard;
areaOfYard = FindTheArea(lengthOfYard, widthOfYard);
cout<< "\nYour yard is ";
cout<< areaOfYard;
cout<< " square meter\n\n";
return 0;
}
USHORT FindTheArea(USHORT l, USHORT w)
{
return (l * w);
}
Output:
Example #3 Function Prototype code snippet
// returns long, has two parameters
long FindArea(long length, long width);
// returns void, has one parameter
void PrintMessage(int messageNumber);
// returns int, has no parameters
int GetChoice();
// returns char, has no parameters
char BadFunction();
Example #4 Function Definition code snippet
long Area(long l, long w)
{
return (l * w);
}
void PrintMessage(int whichMsg)
{
if (whichMsg == 0)
cout << "Hello.\n";
if (whichMsg == 1)
cout << "Goodbye.\n";
if (whichMsg > 1)
cout << "I'm confused.\n";
}
Example #5 The use of local variable and parameters
#include <iostream>
using namespace std;
// a function prototype
float Convert(float);
int main()
{
float TempFer;
float TempCel;
cout<<"Please enter the temperature in Fahrenheit: ";
cin>>TempFer;
TempCel = Convert(TempFer);
cout<<"\n";
cout<<TempFer<<" Fahrenheit = "<<TempCel<<" Celcius"<<endl;
return 0;
}
// a function definition
float Convert(float TempFer)
{
// local variable....
float TempCel;
TempCel = ((TempFer - 32) * 5) / 9;
// return the result to the calling program
return TempCel;
}
Output:
Example #6 Demonstrating local and global variable
#include <iostream>
using namespace std;
// a function prototype
void myFunction();
// a global scope variables
int x = 5, y = 7;
int main()
{
cout<<"x = 5, y = 7, global scope\n";
cout<<"\nx within main: "<<x<<"\n";
cout<<"y within main: "<<y<<"\n\n";
cout<<"Then function call....\n";
myFunction();
cout<< "Back from myFunction...\n\n";
cout<< "x within main again: "<<x<<"\n";
cout<< "y within main again: "<<y<<"\n\n";
return 0;
}
void myFunction()
{
// a local scope variable
int y = 10;
cout<<"\ny = 10, local scope\n"<<"\n";
cout<<"x within myFunction: "<<x<<"\n";
cout<<"y within myFunction: "<<y<<"\n\n";
}
Output:
Example #7 Variable scope within a block
// demonstrates variables scope within a block
#include <iostream>
using namespace std;
// a function prototype
void myFunc();
int main()
{
int x = 5;
cout<<"\nIn main x is: "<<x;
myFunc();
cout<<"\nBack in main, x is: "<<x<<endl;
return 0;
}
void myFunc()
{
// a local scope variable
int x = 8;
cout<<"\nWithin myFunc, local x: "<<x<<endl;
{
cout<<"\nWithin block in myFunc, x is: "<<x;
// another local variable, within block
int x = 9;
cout<<"\nVery local x: "<<x;
}
cout<<"\nOut of block, in myFunc, x: "<<x<<endl;
}
Output:
Example #8
// demonstrates passing by value to a function
#include <iostream>
using namespace std;
// a function prototype
void swap(int x, int y);
int main()
{
int x = 5, y = 10;
cout<<"In main. Before swap, x: "<<x<<" y: "<<y<<"\n";
cout<<"\nThen calling function swap(x, y)...\n";
swap(x, y);
cout<<"\n...back to main. After swap, x: "<<x<<" y: "<<y<<"\n";
return 0;
}
void swap(int x, int y)
{
int temp;
cout<<"\nIn swap function, confirm before swapping, x: "<<x<<" y: "<< y << "\n";
temp = x;
x = y;
y = temp;
cout<<"In swap function. After swapping, x: "<<x<<" y: "<<y<<"\n";
}
Output:
Example #9
// demonstrates multiple return statements
#include <iostream>
using namespace std; // a function prototype
long int Doubler(long int AmountToDouble);
long int main()
{
long int result = 0;
long int input;
cout<<"Enter a number to be doubled: ";
cin>>input;
cout<<"\nBefore Doubler() is called... ";
cout<<"\ninput: "<<input<<" doubled: "<<result<<"\n";
result = Doubler(input);
cout<<"\nBack from Doubler()...\n";
cout<<"\ninput: " <<input<< " doubled: "<<result<<"\n";
cout<<"Re run this program, input > 10000, see the output...\n";
return 0;
}
long int Doubler(long int original)
{
if (original <= 10000)
return (original * 2);
else
{
cout<<"Key in less than 10000 please!\n";
return -1;
}
}
Output:
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Example #10
// demonstrates the use of default parameter values
#include <iostream>
using namespace std;
// a function prototype, width = 25 and height = 1, are default values
int AreaOfCube(int length, int width = 25, int height = 1);
int main()
{
// assigning new values
int length = 100;
int width = 50;
int height = 2;
int area;
area = AreaOfCube(length, width, height);
cout<<"First time function call, area = "<<area<<"\n";
area = AreaOfCube(length, width);
// height = 1, default value
cout<<"Second time function call, area = "<<area<<"\n";
area = AreaOfCube(length);
// width = 25, height = 1, default values
cout<<"Third time function call, area = "<<area<<"\n";
return 0;
}
AreaOfCube(int length, int width, int height)
{ return (length * width * height); }
Output:
Example #11
// demonstrates an inline functions
#include <iostream>
using namespace std;
// an inline function doesn't need prototype here
// directly declares and defines the function
inline int Doubler(int target)
{ return (2*target); }
int main()
{
int target;
cout<<"Enter a number to work with: ";
cin>>target;
cout<<"\n";
target = Doubler(target);
cout<<"First time function call, Target: "<<target<<endl;
target = Doubler(target);
cout<<"Second time function call, Target: "<<target<<endl;
target = Doubler(target);
cout<<"Third time function call, Target: "<<target<<endl;
return 0;
}
Output:
Example #12
// a simple random number function generator...
#include <iostream>
using namespace std;
#include <cdos>
int main()
{
int i;
cout<<"Ten random numbers from 0 to 99\n\n";
for(i=0; i<10; i++)
{
// a random number function generator
cout<<rand()%100<<" ";
// let have 2 seconds delay...
sleep(2);
}
cout<<endl;
return 0;
}
Output:
C and C++ further readings:
- Check the best selling C / C++ books at Amazon.com.
- For this Module purpose, you can check the standard libraries of these various standards of C / C++. Explore and compare the standard functions and their variation if any in the libraries. You can download or read online the specification at the following links. (ISO/IEC is covering ANSI and is more general):
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