ceval

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

Functions accessibe from main()

Function	Argument(s)	Return Value
ceval_result()	A mathematical expression in the form of a character array or a CPP string	The result of the expression as a floating point number
ceval_tree()	A mathematical expression in the form of a character array or a CPP string	The function prints the parse tree with each node properly indented depending on it's location in the tree structure

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 ceval. 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:

git clone https://github.com/erstan/ceval.git /tmp/ceval && \
cd /tmp/ceval && \
sudo make install

Or install the latest release with the clib package manager:

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>
.
.
.