cppreference.com > Standard C String and Character > atof atof Syntax:
      #include <stdlib.h>
      double atof( const char *str );
The function atof() converts str into a double, then returns that value. str must start with a valid number, but can be terminated with any non-numerical character, other than "E" or "e". For example,
       x = atof( "42.0is_the_answer" );
results in x being set to 42.0. Related topics: atoi atol (Standard C I/O) sprintf strtod