Full prototype:
int isdigit(int);
Purpose and Notes:
Tests whether the argument passed to the function is a digit (0-9) and returns a C-style true if it is and a C-style false otherwise.
Returns:
C-style true or false based on whether the argument passed into the function was a digit in which a C-style true is returned. Or if it is not a digit than a C-style false is returned.
Argument 1:
int- Character (including EOF, hence int instead of char) to be tested on whether it is a digit or not.