C++ ClassRoom -- Lecture No. 1

OK!

In C++
We use
//
for one line comments
examples:
//this is a comment
or
int a=5; //a one line comment can come here too without any problems ;)
and /* */
for more lines
example:
/* this is a big comment */
or /* this
is
a
big
comment */
or int a /* OK! The int variable name here is a ;) */ =5; //I know this example is looking ugly but still it's just an example ;)

cout outputs a message to the screen
cin takes in user input

int=integer; //Example: int x = 999;
float=float; //Example: float y = 5.7;
bool=true /* or */ false; //That is exactly like this: bool a=true; bool b=false;
double=double;  //Example: double z = 998894.54982;

Double means "Double precision Floating-point number" while Float means "Floating-point number"

float vs double : double wins because double can take more numbers. For simple numbers like 599.75 always use float but for complicated numbers like 998894.54982 always use double. Why? Because when doing maths in C/C++ using double is like a must because double is more precise than float! Float can round numbers too when the answer is longer than it's storing capacity but usually numbers are not too bigger than double's storing capacity hence always using double when doing maths in C/C++ is better ;)

char is "character" & char is for 1 letter
char a="h";
varchar is "variable characters" & varchar is for up to 4000 letters at once ;)
varchar vc = "Hello World or Hello world or hello World or hello world"
bool is for true or false
bool a=true; //never use bool a="true"; always use bool a=true; because C/C++ does know what is true with bool data type
bool b=false; //never use bool b="false"; always use bool b=false; because C/C++ does know what is false with bool data type

using of const
we can not change value of a constant (that is const)
for example:
const int a=4;
a=3;
this is wrong! Because we can not change the value of a constant after it's declared :(

another example:
int a=4;
a=3;
this is correct! Because we can always change the value of a variable anytime we want ;)

with sizeof()
we take the memory size of a variable
for example:

int a=5;
cout<<sizeof(int);

this will print
4
because int=4 in your computer's memory (or might be different :P)
it is about your computer!
cout<<sizeof(a);
is the same as
cout<<sizeof(int);
because a is declared as an int!
So, the result will be
4
again! Because /*remember*/ a is decalred as an int ;)

#include <iostream>
using namespace std;

int main(int argc, char ** argv) {
 int a=5;
 cout<<sizeof(5);
}

this will print
4
not 5
because 5 is an int
and int=4 in your computer (or might be different :P)
-------
lets  go in "if else" statements now
we declare it as

if(expression) {
    statement1
} else {
    statement2
}

example:

int a=5;
if(a==5){
 cout<<"a is 5";
} else {
 cout<<"a is not 5"
}

also, if we want to check more things
we use "else if"
example:

#include <iostream>
using namespace std;

int main(int argc, char ** argv) {
int a;
cin>>a;
if(a>5) {
cout<<"a is greater than 5";
} else if(a<5) {
 cout<<"a is smaller than 5";
} else {
 cout<<"5";
 }
}

Lecture Ends Here ;)
-------
Challenges Start Here ;)

So,
Challenge is:
Make a program
that declares all variables int, float & most other types
and after putting them

example:
int a;
cin>>a;
cout<<a;
float b;
cin>>b;
cout<<b;

etc....
continue the program (in whatever way you want) & then use everything in the program (take the example above for an example)!
int, bool, char, varchar etc...

--"Owl" & "XRahat2011" Participated In Challenge & Both Succeeded Without Any Mistakes ;)

Challenges Finish Here ;)
-------
HomeWork Starts Here ;)

Make a very simple calculator that can add, subtract, divide & multiply numbers ;)

HomeWork Ends Here ;)
-------
** The End ;)
** Class Moderated By "XRahat2011" ;)