Variable Nomenclature

[appoint_raj]

why in programing language variable names whould start from underscore or alphabetes only and not from a number?

[agent_kiran]

It's a naming convention defined by all the other language developers.

[Singing Boyo]

It's an extremely rigid convention, and they cannot start with numbers for another reason... It's extremely difficult for a compiler to tell the difference if there is a number at the beginning of your variable name. Not so hard after that, but before the compiler knows that is is reading a variable, if you give it what looks like a numerical constant, it will be confused...

[angryboy]

To add to what SB said, imagine you are expected to write a parser and is expected to categorize this into digits or variables:

int 123;
// whatever code here
123 = 999;

That's a headache to work with isn't it.