Learn Function...the hardest way

These program help to understand the concept of function.

Program_1.cpp - simple add program
Program_2.cpp - same add program but using 'function'
Program_3.cpp - program to understand why function (this is question)
Program_4.cpp - Program to understand why function (here is answer)
Program_5.cpp - same program via 'Function not returning a value' (same as Program_2.cpp)(invoke_1)
Program_6.cpp - simple add program via 'Function returning a value'
Program_7.cpp - same program via 'Function not returning a value' (same as Program_5.cpp)(invoke_2)
Program_8.cpp - same program via 'Function not returning a value' (same as Program_7.cpp)(invoke_3)
Program_9.cpp - simple add program via call by value 'function returning a value'
Program_10.cpp - simple add program via call by value 'function not returning a value'
Program_11.cpp - simple add program via call by reference 'function returning a value'
Program_12.cpp - simple add program via call by reference 'function not returing a value'

==================================================================
program_1.cpp
// simple program to add 2 number
#include <iostream>
using namespace std;

int main()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

===================================================================
program_2.cpp 
//same add program but using 'function'
#include <iostream>
using namespace std;

void add()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    add();          //here we are calling (invoking) the function
}

====================================================================
Program_3.cpp
// program_3.cpp and Program_4.cpp is answer of question why function? 
#include <iostream>
using namespace std;

int main()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
   
    int a1=0;
    int b1=0;
    int c1=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a1 >> b1;
   
    c1 = a1 + b1;
   
    cout << "\n Addition of 2 number is: " << c1 << endl;
   
    int a2=0;
    int b2=0;
    int c2=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a2 >> b2;
   
    c2 = a2 + b2;
   
    cout << "\n Addition of 2 number is: " << c2 << endl;
}

==================================================================
Program_4.cpp
// program_3.cpp and Program_4.cpp is answer of question why function?
#include <iostream>
using namespace std;

void add()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    add();
    add();           //here we are calling function 3 time
    add();
}

=========================================================================
 program_5.cpp
// simple program to add 2 number using 'Function not returning a value'
#include <iostream>
using namespace std;

void add()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    add();
}
// This program is same as Program_2.cpp (in case you notice that)

====================================================================
Program_6.cpp 
// simple program to add 2 number using 'Function returning a value'
#include <iostream>
using namespace std;

int add()
{
    int a=0;
    int b=0;
    int c=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    c = a + b;
   
    return (c);
}

int main()
{
    int c;              // Did you notice this
    c = add();         // understand what is going on here
    cout << "\n Addition of 2 number is: " << c << endl;
}

=======================================================================
Program_7.cpp
// This is another way to invoking (calling) a function
// and Program_7.cpp = Program_5.cpp  (please notice the differnce in programs, but both of them doing exact same work.) (but different calling methode)
#include <iostream>
using namespace std;

void add(int a, int b)
{
    int c = 0;
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    int a=0;
    int b=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    add(a, b) ;
}

---------------------------------------------------------------------------------------------
Program_8.cpp
// Yet another ways to calling (invoke) a function
// This Program name is ; by Function not returning a value)
// and Program_8.cpp = Program_7.cpp   (both are not returning a value, but different calling methode)                      
#include <iostream>
using namespace std;

void add(int, int);         //declaration or prototype of function

int main()
{
    int a=0;
    int b=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    add(a, b);
}

void add(int a, int b)         //definition of function
{
    int c = 0;
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

==========================================================
Program_9.cpp
// simple add program via call by value 'function returning a value'
// this is equal to Program_6.cpp
#include <iostream>
using namespace std;

int add(int a, int b)    
{
    int c = 0;
    c = a + b;
  
    return (c);
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
  
    c = add(a, b);   
    cout << "\n Addition of 2 number is: " << c << endl;
}
*/

==========================================================
Program_10.cpp
// simple add program via call by value 'function not-returning a value'
// this is equal to Program_7.cpp
#include <iostream>
using namespace std;

void add(int a, int b)    
{
    int c = 0;
    c = a + b;
  
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
  
    add(a, b);   
}
*/

=================================================================

// This is a extra program to understand 'actual' and 'formal' parameter
// which associated with the 'call by value' and 'call by reference'#include <iostream>
using namespace std;

void add(int a, int b)      //here a, b are formal parameter
{
    int c = 0;
    c = a + b;
  
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
  
    d = a-b+c;          //actual parameter
    cout << " \n substraction is(d): " << d << endl;
  
    add(a, b);     //actual parameter
}

To learn more about 'actual parameter & formal parameter' click here

========================================================================
Program_11.cpp
// simple add program via call by reference 'function returning a value'
#include <iostream>
using namespace std;

int add(int &a, int &b)   
{
    int c = 0;
    c = a + b;
  
    return (c);
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
  
    c = add(a, b);   
    cout << "\n Addition of 2 number is: " << c << endl;
}
 
===============================================================
Program_12.cpp
// simple add program via call by reference 'function not-returning a value'
#include <iostream>
using namespace std;

void add(int &a, int &b)   
{
    int c = 0;
    c = a + b;
  
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
  
    add(a, b);   
}
=========================================================

// why use  'Function returning a value'
#include <iostream>
using namespace std;

int divide()
{
    int a1=0;
    int b1=0;
    int c1=0;
  
    cout << "\n Please Enter 2 number for divide: ";
    cin >> a1 >> b1;
    c1 = a1 / b1;
    return (c1);
}

int add()
{
    int a=0;
    int b=0;
    int c=0;
  
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
    c = a + b;
    return (c);
}

int main()
{
    int c1;
    c1 = divide();
  
    int c;             
    c = add(); 
  
    int d;
    d = c + c1;
    cout << "\n Addition of 2 number is: " << d << endl;
}

program to understand actual parameter and formal parameter

• Formal and actual parameter are associated with the concept of 'call by value' and 'call by reference'
• see the effect of 'call by value' and 'call by reference'

====================================================
//this program to illustrate call_by_reference
#include <iostream>
using namespace std;

int add(int &);

int main()
{
    int a=2;
    int square;
    square = add(a);
    cout << "\n" << a;
    cout << "\n" << square;
}

int add(int &a)
{
    a=a+1;
    return(a*a);
}

OUTPUT:
3
9


====================================================== 
// this program to illustrate call_by_value
#include <iostream>
using namespace std;

int add(int);

int main()
{
    int a=2;
    int square;
    square = add(a);
    cout << "\n" << a;
    cout << "\n" << square;
}

int add(int a)
{
    a=a+1;
    return(a*a);
}

OUTPUT:
2
9 

======================================================
// This is a extra program to understand 'actual' and 'formal' parameter
// which associated with the 'call by value' and 'call by reference'
#include <iostream>
using namespace std;

void add(int a, int b)      //here a, b are formal parameter
{
    int c = 0;
    c = a + b;
   
    cout << "\n Addition of 2 number is: " << c << endl;
}

int main()
{
    int a=0;
    int b=0;
    int c=0;
    int d=0;
   
    cout << "\n Please Enter 2 number: ";
    cin >> a >> b;
   
    d = a-b+c;          //actual parameter
    cout << " \n substraction is(d): " << d << endl;
   
    add(a, b);     //actual parameter
}

program to find GCD using recursion

//also help to understand the command line argument

#include <stdio.h>
#include <stdlib.h>

int gcd(int, int);

int main(int argc, const char* argv[])       //command line argument
{
    int a, b;
    a = atoi(argv[1]);
    b = atoi(argv[2]);
   
    printf("The greatest commaon divisor of %d and %d is %d\n", a, b, gcd(a,b));
    return 0;
}

int gcd(int a, int b)
{
    if (b == 0)
        return a;                   //recursion implementation
    else
        return gcd(b, a % b);
}

 

A simple program to understand recursion

#include <stdio.h>
#include <conio.h>

void recTest(int i)
{
    if(i > 0)
    {
        recTest(i - 1);          //understand this crazy little insane item
        printf("%i\n", i);
    }
}

int main()
{
    recTest(5);
}

OUTPUT:
1
2
3
4
5

Program to check ARMSTRONG number in c++

// program to check the armstrong number

#include <iostream>
using namespace std;

int main()
{
   int num, sum = 0, temp, remainder;

   cout << "Enter a number to check: " << endl;     
   cin >> num;

   temp = num;

   while( temp != 0 )
   {
      remainder = temp%10;
      sum = sum + remainder*remainder*remainder;
      temp = temp/10;
   }

   if ( num == sum )
      cout << "Your Number is an armstrong number." << endl;
   else
      cout << "Your Number is not an armstrong number." << endl;      
}
___________________________________________________________________________________

//program to generate armstrong number

#include <iostream>
using namespace std;

int main()
{
   int r;
   long long number = 0, c, sum = 0, temp;

   cout << "Enter the maximum number upto which you want to find armstrong numbers ";
   cin >> number;

   cout << "Following armstrong numbers are found from 1 to " << number << endl;

   for( c = 1 ; c <= number ; c++ )
   {
      temp = c;
      while( temp != 0 )
      {
         r = temp%10;
         sum = sum + r*r*r;
         temp = temp/10;
      }

      if ( c == sum )
         cout << c << endl;
      sum = 0;
   }
}

Give a one-line C expression to test whether a number is a power of 2

Ans. //( (x > 0) && ((x & (x - 1)) == 0) )

#include <iostream>
using namespace std;

int main()
{
    int x;
    cout << "enter the no of : ";
    cin >> x;
   
    if( (x > 0) && ((x & (x - 1)) == 0) )
    {
        cout <<"no is power of 2";
    }
   
    else
    {
        cout <<"no is not a power of 2";
    }
   
}

Program to find whether the number is power of 2 or not?

//without  using  functions.

#include <stdio.h>
#include <conio.h>

int main()
{
    int num, rem, flag=0;
    printf ("\n Enter a Number: ");
    scanf ("%d", &num);
   
    while(num > 2)
    {
        rem = num % 2;
        if( rem == 1 )
        {
            flag = 1;
            break;
        }
        else
        num = num/2;
    }
   
    if( flag == 1 )
    {
        printf("\n Number is not Power of two.");
    }
    else
    {
        printf("\n Number is Power of two");
    }
}

A program to print febonacci series upto first 20 trems

#include <stdio.h>
#include <conio.h>

int main()
{
    int a = 0;
    int b = 1;
    int i,sum;
    
    for(i = 0;i<20;i++)
    {
        sum = a+b;
        printf("%d\n",sum);
         
        a = b;
        b = sum;
    }
}

A program to print the FIBONACCI series

#include<iostream>
using namespace std;

main()
{
   int n, c, first = 0, second = 1, next;

   cout << "Enter the number of terms of Fibonacci series you want" << endl;
   cin >> n;

   cout << "First " << n << " terms of Fibonacci series are :- " << endl;

   for ( c = 0 ; c < n ; c++ )
   {
      if ( c <= 1 )
         next = c;

      else
      {
         next = first + second;
         first = second;
         second = next;
      }
      cout << next << endl;
   }
}

Program to understand Do While loop

//The body of the loop will be executed at least once before the condition is checked
#include<iostream>
#include<string>
using namespace std;

int main()
{
    string password;
   
    do
    {
        cout << "Enter your password: ";
        cin >> password;
    }
   
    while (password != "foobar");         //notice semicolon
    cout << "welcome, you enterted right password";
}

Factorial of a number using class in cpp

//This program is compiled using GCC

#include<iostream>
using namespace std;

class factorial
{
    int num;
   
    public:
        void getinfo()                 //1st member function of class factorial
        {
            cout << "\n Enter the number for which the factorial is to be found: ";
            cin >> num;
        }
       
        void facto()           //2nd member function of class factorial        
        {
            int i, fact=1;
           
            if(num == 0 || num == 1)
            {
                cout << "\n factorial of "<< num << " is 1";
            }
           
            else
            {
                for(i=1; i<=num; i++)
                {
                    fact = fact*i;
                }
                cout << "\n factorial of " << num << " is: " << fact;
            }
        }
};

int main()
{
    factorial f1;                //creating the object of class 'factorial'
    f1.getinfo();
    f1.facto();
   
    cin.ignore();      //these 2 fun are use
    cin.get();          //for holding the output screen
}

Concept of global and global declaration

//program to illustrate the concept of global variable
#include <iostream>
using namespace std;

int myint;       //this is the declaration of global variable

void another_function()
{
    myint = 12345;
}

int main()
{
    cout << myint << endl; 

    myint = 10;
    cout << myint << endl;
 
    another_function();
    cout << myint << endl;
}

output:
0                         //because cpp compiler define global variable to 0; if they r not declared
10
12345 
_______________________________________________________________
//program to illustrate global declaration concept
#include <iostream>
using namespace std;

struct int_holder
{
    int my_int1;
    int my_int2;
    double my_double;
};

int main()
{
    int_holder holder;
    cout << holder.my_int1 << endl;
    cout << holder.my_int2 << endl;
    cout << holder.my_double << endl;
} 

output: 
200044456             //these all 3 are garbage value assign by compiler
-12324924
1.4345345  
_________________________________________________________________
//program to illustrate global declaration concept
#include <iostream>
using namespace std;

struct int_holder
{
    int my_int1;
    int my_int2;
    double my_double;
};

int_holder holder;           

int main()
{ 
    cout << holder.my_int1 << endl;
    cout << holder.my_int2 << endl;
    cout << holder.my_double << endl;
}  

output: 
0                    //value 0 is assign by compiler because declaration is global
0
0 
----------------------------------------------------------------------------------------------

 //More example to understand concept of Global variable
#include <iostream>
using namespace std;

int example(int x)
{
    x = x+3;
    return x;
}

int main()
{
    int x = 5;
    cout << example(x) << "\t" << x;
}


#include <iostream>
using namespace std;

 int x = 6;   //this global variable now available to every function

int example()
{
    x = x+3;
    return x;
}

int main()
{
    cout << example() << "\t" << x;
} 
 

A program To find out smallest number in an array

#include <stdio.h>
#include <conio.h>

int main()
{
    int n, i, min;

    printf ("\nEnter Total Numbers Of Numbers In The Array: ");
    scanf ("%d",&n);

    int array[n];

    for(i=0; i<n; i++)
    {
        printf ("\nEnter %d Number: ",i+1);
        scanf ("%d",&array[i]);
    }

    min = array[0];

    for(i=0; i<n; i++)
    {
        if(array[i] < min)

        min = array[i];
    }

    printf("\nThe Smallest Number in the array is %d \n",min);    
}

A program to find largest number in an given array

#include <stdio.h>
#include <conio.h>

int main()
{
    int n, i, max;

    printf ("Enter Total Numbers Of Numbers In The Array: ");
    scanf ("%d",&n);

    int array[n];
   
    for( i=0; i<n; i++)
    {
        printf ("\nEnter %d Number: ",i+1);
        scanf ("%d",&array[i]);
    }

    max = array[0];

    for(i=0;i<n;i++)
    {
        if(array[i] > max)

        max = array[i];
    }
    printf ("\nThe Largest Number in the array is %d ",max);    
}

'c++ struct' can have private_members and function also

//A Simple program to show c++ structure can have function
// using c++, GCC complier
 
#include <iostream>
using namespace std;

struct CRectangle       //here we define a user-defined-datatype using 'struct'
{
    private:
        int x, y;

    public:
        void set_values (int,int);

        int area()
        {
            return (x*y);
        }
};

void CRectangle :: set_values (int a, int b)
{
    x = a;
    y = b;
}

int main()
{
    CRectangle rect;    //creating the object (rect) of a class (CRectangle)

    rect.set_values (3,4);
    cout << "area:" << rect.area();
   
    cin.ignore();
    cin.get();
}
______________________________________________________________
also see the same program using class (only difference, we use 'class' instead of 'struct')

A program to print multiplication table from 1 to 10

#include <stdio.h>
#include <conio.h>

int main()
{
    int i,j;

    int array[10][10];
    
    for(i=0; i<10; i++)
    {
        for(j=0; j<10; j++)
        {
            array[i][j] = (i+1)*(j+1);
        }               
    }
    
    for(i=0; i<10; i++)
    {
        for(j=0; j<10; j++)
        {   
            printf("%3d ",array[i][j]);
        }
        printf("\n");
    } 
}

A simple program to understand classes in C#

using System;

class building
{
    public int floors;   //number of floors         //C# class doesn't support 'public :'
    public int area;     //total square footage of building
    public int occupants;  //number of occupants
}

class building_Demo
{
    public static void Main()
    {
        building house = new building();  //create a bbuilding object
        int areaPP;    //area per person
      
        //assign values to fields to fields in house
        house.occupants = 4;
        house.area = 2500;
        house.floors = 2;
  
    //compute the area per person
    areaPP = house.area/house.occupants;
  
    Console.WriteLine("house has:\n "+
                       house.floors + " floors\n "+
                       house.occupants + " occupants\n "+
                       house.area + " total area\n "+
                       areaPP + " area per person");
    }
}

OUTPUT:
 house has:
  2  floors
  4  occupants
  2500  total area
  625 area per person

A simple 'class' program

//class with single object
// using c++
#include <iostream>
using namespace std;

class CRectangle  //here we define a user-defined-datatype 'CRectangle' using 'class'
{
    private:
        int x, y;

    public:
        void set_values (int,int);

        int area()
        {
            return (x*y);
        }
};

void CRectangle :: set_values (int a, int b)
{
    x = a;
    y = b;
}

int main()
{
    CRectangle rect;    //creating the object (rect) of a class (CRectangle)

    rect.set_values (3,4);
    cout << "area:" << rect.area();
   
    cin.ignore();
    cin.get();
}

Note: we must use the operator scope-resulation (::) to specify that we are defining a function that is a member of the class CRectangle and not a regular global function.
 _________________________________________________________
See also the same program using struct (only difference, we use 'struct' instead of 'class') 

A simple 'struct' program

// simple struct (user defined datatype) program
// using c++

#include <iostream>
using namespace std;

struct student                 //student is user defind data type
{
    int roll_no;
    char name;
    int age;
};

int main()
{
    student a;              //a is the object of student

    cout << "\nEnter the name of student: ";
    cin >> a.name;

    cout << "\n Enter your age: ";
    cin >> a.age;

    cout << "\n enter your roll no: ";
    cin >> a.roll_no;
   
    cout << "\n student name is :" << a.name;
    cout << "\n               age is :" << a.age;
    cout << "\n               roll no :" << a.roll_no;
   
}

Program to find factorial using recursion in c

//1st way
#include <stdio.h>
#include <conio.h>

int fact(int);

int main()
{
    int num, f;
    printf ("\n Enter a number: ");
    scanf ("%d", &num);
    f = fact(num);
    printf (" \n Factorial of %d is: %d ", num, f);
}

int fact(int n)
{
    if(n == 1)
    {
        return 1;
    }
   
    else
    {
        return (n*fact(n-1));
    }
}
____________________________________________________________________
//2nd way
#include <stdio.h>
#include <conio.h>

int getFactorial(int n)
{
    int local;
    if (n > 1)
    {
        local = n * getFactorial(n-1);
        return local;
    }
    else
        return 1;
}

int main()
{
    int num, f;
    printf ( "\n Enter a number: " );
    scanf ("%d", &num);
    f = getFactorial(num);
    printf ( "\n Factorial of %d is: %d ", num, f);
}