Declare a variable

Only once declaration.

You have the option to assign a value to the variable at the time you declare the variable or to declare it and assign a value later.

int a=10;

int b;
b=11;

Any variable declared with the auto keyword should be initialized at the time of its declaration or there will be an error.

auto c=13;

// error
// auto d;

constant

A constant is an expression with a fixed value. It cannot be changed while the program is running. Use the const keyword to define a constant variable.

const int X = 42;

All constant variables must be initialized at the time of their creation.