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A C/C++ library for parsing and evaluation of arithmetic expressions.

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# ceval
A C/C++ header for parsing and evaluation of arithmetic expressions.

## Functions accessibe from main()
<table>
<thead><th>Function</th><th>Argument(s)</th><th>Return Value</th></thead>
<tbody>
 <tr>
  <td><code>ceval_result()</code></td>
  <td>A mathematical expression in the form of a character array or a CPP string</td>
  <td>The result of the expression as a floating point number</td>
</tr>
<tr>
  <td><code>ceval_tree()</code></td>
  <td>A mathematical expression in the form of a character array or a CPP string</td>
  <td>The function prints the parse tree with each node properly indented depending on it's location in the tree structure</td>
</tr>
</tbody>
</table>

## Supported expressions
Any valid combination of the following operators and functions, with floating point numbers (in decimal or exponential form) as operands can be parsed by <b>ceval</b>. Parentheses can be used to override the default operator precedences.

* Arithematic operators

`+` (addition), `-` (subtraction), `*` (multiplication), `/` (division), `%` (modulo), `**` (exponentiation), `//` (quotient)
* Relational operators

`==` (equal), `!=` (not equal), `<` (strictly less), `>` (strictly greater), `<=` (less or equal), `>=` (greater or equal) to compare the results of two expressions

* Single-argument functions

`exp()`, `sqrt()`, `cbrt()`, `sin()`, `cos()`, `tan()`, `asin()`, `acos()`, `atan()`, `sinh()`, `cosh()`, `tanh()`, `abs()`, `ceil()`, `floor()`, `log10()`, `ln()`, `deg2rad()`, `rad2deg()`, `signum()`, `int()`, `frac()`, `fact()`

* Two-argument functions

`pow()`, `atan2()`, `gcd()`, `hcf()`, `lcm()`, `log()` (generalized log(b, x) to any base `b`)

* Pre-defined math constants

`pi`, `e`

* Logical operators

`&&`, `||` and `!`
 
* Bitwise operators

`&`, `|`, `^`, `<<`, `>>`, `~`

* Other operators

* `,` (Comma operator)
  Comma operator returns the result of it's rightmost operand
  Ex: `2,3` would give `3`; `4,3,0` would be equal to `0`; and `cos(pi/2,pi/3,pi)` would return `cos(pi)` i.e, `-1`

## Installation
From source:

```shell
git clone https://github.com/erstan/ceval.git /tmp/ceval && \
cd /tmp/ceval && \
sudo make install
```
<b>Or</b> install the latest release with the [clib](https://github.com/clibs/clib) package manager:
```shell
clib install erstan/ceval -o /tmp/ceval
```

## Usage
After the installation, just include the ceval library using `#include<ceval/ceval.h>` directive in your C/C++ project.

The code snippet given below is a console based interpreter that interactively takes in math expressions from stdin, and prints out their parse trees and results.

```
//lang=c
#include<stdio.h>
#include<stdlib.h>

#include<ceval/ceval.h>

int main(int argc, char ** argv) {
  char expr[100];
  while (1) {
    printf("In = ");
    fgets(expr, 100, stdin);
    if (!strcmp(expr, "exit\n")) {
      break;
    } else if (!strcmp(expr, "clear\n")) {
      system("clear");
      continue;
    } else {
      ceval_tree(expr);
      printf("\nOut = %f\n\n", ceval_result(expr));
    }
  }
  return 0;
}
```
The same interpreter can be implemented in C++ as follows
```
//lang=cpp
#include<iostream>
#include<cstdlib>
#include<string>

#include<ceval/ceval.h>

int main(int argc, char ** argv) {
  std::string expr;
  while (1) {
    printf("In = ");
    std::cin >> expr;
    if (expr=="exit") {
      break;
    } else if (expr=="clear") {
      system("clear");
      continue;
    } else {
      ceval_tree(expr);
      std::cout << "\nOut = " << ceval_result(expr) << "\n\n";
    }
  }
  return 0;
}
```
## Test Run
```
In = 3*7**2
                2
        **
                7
*
        3

Out = 147.000000

In = (3.2+2.8)/2
        2
/
                2.80
        +
                3.20

Out = 3.000000

In = e**pi>pi**e
                e
        **
                pi
>
                pi
        **
                e

Out = 1.000000

In = 5.4%2
        2
%
        5.40

Out = 1.400000

In = 5.4//2
        2
//
        5.40

Out = 2.000000

In = 2*2.0+1.4
        1.40
+
                2
        *
                2

Out = 5.400000

In = (5/4+3*-5)+(sin(pi))**2+(cos(pi))**2
                2
        **
                        pi
                cos
+
                        2
                **
                                pi
                        sin
        +
                                        5
                                -
                        *
                                3
                +
                                4
                        /
                                5

Out = -12.750000

In = 3,4,5,6
        6
,
                5
        ,
                        4
                ,
                        3

Out = 6.000000

In = tanh(2/3)==(sinh(2/3)/cosh(2/3))
                                3
                        /
                                2
                cosh
        /
                                3
                        /
                                2
                sinh
==
                        3
                /
                        2
        tanh

Out = 1.000000

In = (2+3/3+(3+9.7))
                9.70
        +
                3
+
                        3
                /
                        3
        +
                2

Out = 15.700000

In = sin(pi/2)+cos(pi/2)+tan(pi/2)
                        2
                /
                        pi
        tan
+
                                2
                        /
                                pi
                cos
        +
                                2
                        /
                                pi
                sin

[ceval]: tan() is not defined for odd-integral multiples of pi/2

Out = nan

In = asin(2)
        2
asin

[ceval]: Numerical argument out of domain

Out = nan

In = exit
... Program finished with exit code 0

```
## Stoic mode
The inbuilt functions in `ceval` print out error messages to stdout when some syntactical anomaly is encountered during the parsing and evaluation process. To suppress the error messages, define the `CEVAL_STOICAL` macro before including the library in a C/C++ project. In the stoic mode, problematic expressions are evaluated to `nan`. 
```
#define CEVAL_STOICAL
#include<ceval/ceval.h>
.
.
.
```

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