Case Sensitivity in C++
C++ is case-sensitive. In other words, uppercase and lowercase letters are considered to be different. A variable named age is different from Age, which is different from AGE.
NOTE: Some compilers allow you to turn case sensitivity off. Don't be tempted to do this; your programs won't work with other compilers, and other C++ programmers will be very confused by your code.
There are various conventions for how to name variables, and although it doesn't much matter which method you adopt, it is important to be consistent throughout your program.
Many programmers prefer to use all lowercase letters for their variable names. If the name requires two words (for example, my car), there are two popular conventions: my_car or myCar. The latter form is called camel-notation, because the capitalization looks something like a camel's hump.
Some people find the underscore character (my_car) to be easier to read, while others prefer to avoid the underscore, because it is more difficult to type. This book uses camel-notation, in which the second and all subsequent words are capitalized: myCar, theQuickBrownFox, and so forth.
NOTE: Many advanced programmers employ a notation style that is often referred to as Hungarian notation. The idea behind Hungarian notation is to prefix every variable with a set of characters that describes its type. Integer variables might begin with a lowercase letter i, longs might begin with a lowercase l. Other notations indicate constants, globals, pointers, and so forth. Most of this is much more important in C programming, because C++ supports the creation of user-defined types and because C++ is strongly typed.