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The header <math.h> declares mathematical functions and macros.
The macros EDOM and ERANGE (found in <errno.h>) are non-zero integral constants that are used to signal domain and range errors for the functions; HUGE_VAL is a positive double value. A domain error occurs if an argument is outside the domain over which the function is defined. On a domain error, errno is set to EDOM; the return value is implementation-defined. A range error occurs if the result of the function cannot be represented as a double. If the result overflows, the function returns HUGE_VAL with the right sign, and errno is set to ERANGE. If the result underflows, the function returns zero; whether errno is set to ERANGE is implementation-defined. (more…)

The header <stdlib.h> declares functions for number conversion, storage allocation, and similar tasks. double atof(const char *s)
atof converts s to double; it is equivalent to strtod(s, (char**)NULL).
int atoi(const char *s)
converts s to int; it is equivalent to (int)strtol(s, (char**)NULL, 10).
long atol(const char *s)
converts s to long; it is equivalent to strtol(s, (char**)NULL, 10). (more…)

The assert macro is used to add diagnostics to programs: (more…)

The header <stdarg.h> provides facilities for stepping through a list of function arguments of unknown number and type.
Suppose lastarg is the last named parameter of a function f with a variable number of arguments. Then declare within f a variable of type va_list that will point to each argument in turn:

   va_list ap;
ap must be initialized once with the macro va_start before any unnamed argument is accessed:
  va_start(va_list ap, lastarg);
Thereafter, each execution of the macro va_arg will produce a value that has the type and value of the next unnamed argument, and will also modify ap so the next use of va_arg returns the next argument:
  type va_arg(va_list ap, type);
The macro

   void va_end(va_list ap);
must be called once after the arguments have been processed but before f is exited