What's the difference between int a; int b = 42; a = 10; b = 3;

Question

declaring a variable type and without declaring a variable type

Answer 1

We must declare variable types in c++ because it is a type safe programming language. And computers aren't smart enough to understand what we are meaning.

Example:
char c = 'c';
string s = "s";

Computers won't understand the difference. That's why you must specify the types.

Answer 2

You must declare variable type then you can assign it a value. Once You declare a variable then you can assign it values as many times as you can but you can't assign a value to a variable whose variable type is not declared.

Answer 3

It depends on which programming languages you use.

In C#

int a;
// it means 'a' = 0 by default;

int b = 42;

a = 10;
// it means the value of 'a' becomes 10, it replaces initial value of 0.

b = 3;
// it means the value of 'b' becomes 3 than 42 now.

----------------------------------------------------------------------------------------------
it is like in Stack which store Variables,

when you declare int a with no value but it sets the initial value to 0, it means

---------
| int |
---------
| a = 0 |
---------

in somewhere (I don't know where is the memory address though :D), Integer type variable named a is created with default value 0.

int b = 42; // it is set up in Stack as

----------
| int |
----------
| b = 42 |
----------

so when you replace a = 10, it becomes as
---------
| int |
---------
| a = 10 |
---------

it replaces the value in Stack with 10, not 0 anymore.

b = 3;

----------
| int |
----------
| b = 42 |
----------

becomes

---------
| int |
---------
| b = 3 |
---------

now.

Answer 4

Kk thnks