Understand the ++ and -- operator

//Please don't copy-paste this program ; make your own implementation
#include <cstdio>
#include <iostream>
using namespace std;

int main()
{
    int a;
    a = 5;
    cout << ++a << endl; // pre-increment -- 6
    cout << --a << endl; // pre-decrement -- 4
    cout << a++ << endl; // post-incremenr -- 5
    cout << a-- << endl; // post-decrement -- 5
   
    cout << a++ << a++ << endl; // 5 -(+1)-> 6
   
    cout << a++ + a++ + a++ << endl ; // 5 -(+1)-> 6 -(+1)-> 7 = 18
   
    //This goes left-to-right
    cout << a++ + a++ + --a; // 5 -(+1)-> 6 -(+1)-> 7 (-1) -->6 =17
   
    // it goes right-to-left
    cout << a++ , a++ , a++;  //7, <-(+1)- 6, <-(+1)- 5
   
    //it goes 1st right-to-left and then left-to-right
    cout << a++ + a++ + a--, ++a; // 21,6
   
    printf ( "%d %d %d %d %d\n",x++, x--, ++x, --x, x++);  // 5 6 6 5 5
   
    //For Practice
    int b = 5, c = 5, i, j, j1;
    i = a++ + a++ + a++;               
    j = ++b + ++b + ++b;
    j1 = c++ + c++ + c--;
   
    printf ("\n value of i using printf:%d\n", i);
    cout << "\n Value of  i : " << i << endl
          << "\n Value of  j : " << j << endl
          << "\n Value of j1 : " << j1 << endl;
       
    printf("value of 1st print is: %d\n", 59);
    printf("value of 2nd print is: %c\n\n", 59);
}
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//What is the output of this program
#include <stdio.h>
int main()
{
    int x=20,y=35;

    x=x++ + y++;

    y=++x + ++y;

    printf ( "%d, %d", x,y);
    return 0;
}

The output for your program is 57, 94.

Explanation:
x = 20, y = 35

x = x++ + y++ = 20 + 35 (x and y would be incremented after the addition) = 55
x++ -----> x = 55 + 1 = 56
y++ -----> y = 35 + 1 = 36

++x -----> x = 56 + 1 = 57 (x and y would be incremented
++y -----> y = 36 + 1 = 37 before the addition)
y = ++x + ++y = 57 + 37 = 94

Hence final values of x and y are 57 and 94 respectively. 

Understand this way:
d=x++; //the value of x is stored to d and d is increment by 1.x remains the same.d=20 x=21
printf ("%d %d",d,x);   // 20 21

x = x++;     
printf("%d",x);    //21

d = x++ + 1; 
x = x++ + 1;   
printf("%d %d");     //d=21 x=22 
d=++x; //here increment is done first after that value is stored=x=21

For further detail click here.

Escape Sequences in c++

#include <cstdio>
#include <iostream>

int main()
{
    // escape sequence covered - \' \" \? \\ \0 \a \b \n \r \t
    printf("\n 1. sandeep \t dheeraj\n");

    printf("\n 2. sandeep \v dheeraj\n");
 

    printf("\n 3. sandeep \r dheeraj\n");
 

    printf("\n 4. sandeep \a\a\a dheeraj\n");
 

    printf("\n 5. sandeep\b dhe\0eraj extra\n");
 

    printf("\n 6. \'sandeep\' \\ \n");  // used \' \" \\
 

    printf("\n 7. Ram? \n");
 

    printf("\n 8. Ram\? \n");    //why we use \? this escape sequence
 

    printf("\n 9. \"dheeraj\" \n");
}

OUTPUT:

For further detail click here.

C++ 'in class variable' and 'static variable' initialization

#include <iostream>
using namespace std;

class Demo
{
  public:
  int a  = 1;
    // static int b=2;  //this gives error
  static int b;
};

int Demo::b=2;  //initialize the static variable of class

int main()
{
    Demo d;
    cout << "\n value of variable a: " << d.a << endl;
    cout << "\n value of static variable b: " << Demo::b << endl;
}

OUTPUT:

Simple Program to find out Prime Number

//c program to find prime number
#include<stdio.h>
#include<conio.h>

int main()
{
    int num, count=0, i;
    printf ( "enter your number:" );
    scanf ( "%d" ,&num);
   
        for(i=1; i<=num; i++)
        {
            if (num%i==0)
            {
                count++;
            }
        }
       
        if (count <= 2)
        {
            printf ("number is prime");
        }
       
        else
        {
            printf ("number is not prime");
        }
    return 0;
}

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//c++ program to find prime number
#include <iostream>
using namespace std;

int main()
{
    int num, count=0, i;
    cout << "\n enter your number: ";
    cin >> num;
   
    if (num==1)
    {
        cout << "\n 1 is a prime number";
    }
   
    else
    {
        for(i=1; i<=num; i++)
        {
            if (num%i==0)
            {
                count++;
            }
        }
       
        if (count==2)
        {
            cout << "number is prime";
        }
       
        else
        {
            cout << "number is not prime";
        }
    }
    return 0;
}