What is auto declaration in C?

Auto is one of the four storage classes in c. This is the default storage class. The auto storage class can be used only inside functions, i.e. only to declare local variables and not to declare global variables. All the local variables are by default auto variables.

Other storage classes are:

Register - variables declared may get stored in CPU registers instead of RAM

Static - default storage class for global variables

extern - defines global variables that is visible to all object modules