A custom Library that can parse and evaluate Mathematical functions accepted as strings

It's a basic C library that supports functions helpful for parsing and evaluating any mathematical expression entered as a string of characters.
Currently this supports only Real numbers.
No build system is needed. Simply copy the appropriate headers and C files into the project and use the functions.
The library has been tested on over a hundred test cases and the results turned out to be fairly accurate upto 4 decimal cases on most test cases.

Key things to keep in consideration while using this library:

• Division operation has been assigned greater priority than multiplication. So the the order of operation around consecutive multiplication and division has to be explicitly specified by the use of parantheses.
• The order of operation has to be explicitly specified if same operator is being consecutively used for more than once.
• Supported funtions:
  • sin, cos, tan, cot, cosec, sec
  • arcsin, arccos, arctan, arccot, arccosec, arcsec
  • ln(natural logarithm), log(base 10 logarithm)
  • fact(factorial), gamma

---

Lexer

Stack *lex(char *inputString);  

The Lexer recognizes 4 different kinds of Tokens:

• Variable 'x'
• Decimal numerals
• Parantheses
• Elementary functions (sin, cos, ln, etc)

---

rpnArrayParser

Stack *parser(token *linkedlistHead);  

The parser scans through the linked list of lexical tokens generated by our lexer and derives a dynamic array of elements arranged in Reverse Polish Notation (postfix nota tion).

The shunting yard algorithm is employed to achieve this task.

---

rpnArrayEval

double eval(Stack* postfixArray, double x0);

A very simple recursive algorithm though memory heavy and slow.

• Sequentially Scans across the received Array of tokens.

• If a sub-array of the form |operand | operand | operator | or |operand | function | is found,evaluate,
  store in a token of type numeral. Push the token into stackA.

• In case three elements don't form the defined subarray, simply push consecutively.

• Repeat steps 2-3 untill all tokens have been scanned.

• Use stackA as the new Array of tokens and repeat steps 1-3 but using stackB for the intended purpose
  of stackA in step 2.

• Empty stackA ans repeat steps 1-5 untill the stack has a single element. !!