atobool - convert ASCII to BOOLEAN value
BOOLEAN atobool (sptr)
This function converts a string pointed to by sptr to a boolean value. Atobool converts the string with the format returned by getfbool(C-3).
A BOOLEAN format has two specifiers. If the string sptr matches the first specifier, a TRUE (nonzero) value is returned. All other strings return a FALSE (zero) value. Partial matches are also considered valid. For example, if the specifier is yes, strings of y, ye, and yes are all valid.
C/Base Reference Manual Chapter 13, "Formatting Data Values"
Strings are compared case insensitive (i.e., Y, YE,
YES, and Yes are also valid for the previous example).