Overview

This is a simple library I've put together for evaluating arithmetic expressions. A user supplies the expressions as a string of characters, and the integer result is placed in the referenced variable.

Features

• Parser for arbitrary arithmetic expressions including signed and unsigned integers, operators, and nested parentheses
• Parser respects order of operations
• Comprehensive testing
• Randomly generated (deterministic) tests
• Error checking for malformed expressions and divide by zero
• Library usage example
• Support for arbitrary length expressions
• Designed to be used as a library
• Simple, heavily annotated header file
• No dependencies
• Debugging output to print out token lists

Usage

Here is an example that shows how to use this library.

#include <stdio.h>
#include <stdlib.h>

#include "eval.h"

int main() {
  int result = 0;
  int return_value = eval("1+2", &result);
  if (return_value == 0) {
    printf("Answer: %d\n", result);
  } else {
    printf("Expression could not be evaluated.\n");
  }
}

One way to build this code would be the following command:

gcc example.c build/eval.o -I src/ -lm

See the Makefile for more details.

Debug

The eval_debug() function is included in this library which works just like eval() but prints internal status messages to stdout.

Here is an example of what one of these messages might look like:

Evaluating: "1+(2 * 3)"
Found digit: 1
Found operator: +
Found paren: (
Found digit: 2
Found operator: *
Found digit: 3
Found paren: )


Begin Token List:
PA (nil) SE 0x5560eade2810 CH 0x5560eade2850 HEAD 0
PA 0x5560eade2810 SE 0x5560eade2850 CH 0x5560eade2910 NUMBER 7
PA 0x5560eade2850 SE 0x5560eade2910 CH (nil) TAIL 0
END Token List:

Function exited successfully.
Answer: 7

Limitations

This library can't presently handle floating point numbers, and will return FAILURE if one is encountered.

Return Value

eval returns SUCCESS (0) if the string was successfully evaluated, and FAILURE (-1) otherwise. Please note that even in the case of failure, the function will still make a best-effort attempt to evaluate the string which can result in unexpected outcomes. For instance, if it is supplied the string "2.2+1", it will drop the '.' and evaluate the string as "22+1".

Dependencies:

The library has no external dependencies. All you need is the C compiler that you are using to compile the host code. To build the examples you need gcc and make.

Test:

make test will run the test program. You should get a result that looks like this:

0 - 1 + 1=2=2
0 - 1 + 1=2=2
0 - 1 - 1=0=0
0 - 5334 - 3452 * 223 - 342 / 5=-764530=-764530
0 - 5 - 3 * 2 - 3 / 5=-1=-1
0 - (1)=1=1
0 - (1 + 1) * 2=4=4
0 - (1 + 1) * (5 * 5) / 4=12=12
0 - 2 + 0 - (6) * 1 * 5 + 5 * 4 + (7 / 6 - (5))=-12=-12
0 - 2 + 0 - (6) * 1 * 5 + 5 * 4 + (7 / 6 - (5)) - 6 * 9 * 3 / 7 - 4 - 5 - 2 - 5 / 4 * 7 - (4) * 4 / 3 / 1 - 7 / (8) * (6) * (8 * 8) + 4 / 3 * (1) + 4 + 9 + 2 + 0 * (6 / 8 * 9 - 2) - 6 - 6 / 4 + 9 / 5 - 0 * 4 / 8=-48=-48
0 - 862 + 170 - (996) * 281 * 305 + 925 * 84 + (327 / 336 - (505)) - 846 * 729 * 313 / 857 - 124 - 895 - 582 - 545 / 814 * 367 - (434) * 364 / 43 / 750 - 87 / (808) * (276) * (178 * 788) + 584 / 403 * (651) + 754 + 399 + 932 + 60 * (676 / 368 * 739 - 12) - 226 - 586 / 94 + 539 / 795 - 570 * 434 / 378=-85465336=-85465336
0 - (1+1+1)^2=9=9
0 - 2^3=8=8
0 - (1 + (1))=2=2
0 - (1 + (1) + 1) + 1=4=4
0 - (160 * 21 + 135 - 43 - 51 - 101 * 100 / 15)=2728=2728
0 - 592 * 179 + 286 + 610 * (328) / 750 / 429=106254=106254
0 - (((29 / 537 + 434 * 264) * 95 - 415 * 71 / 139 + 92 + 133 - 312 + 540) / 405 / 268 / 198 + 242 * (137) / 285 - 192 + (249 - 183 / 140 / 490) * 31 + 249 / (2) * 350 / 7 + (107) / 444 - 451 - 39 + 341 - 244 + 205 + 338 / 116)=13657=13657
0 - ((404) * 154 * 243) / (248 + 786 * 690 * 128)=0=0
0 - 16 + 102 - (47) * 42 / 37 - (80) / ((151 / 55)) / 83 - 140 / 11 - 7 + 12 / 102 - 10 + 38 / 73 * 18 / 42 - 129 - (54) / (32) * (119 - 157 / 33 + 119 * 62 - 134 * (47)) - ((132)) + (140) / 64 + 75 * 28 / 106 - (112) * 108 / 24 * 94 - 117=-48892=-48892
0 - 101 / 44 + 144 / 108 / 165 / 87 * 163 / 108 * (53 * 27 / 22 + 123) / 69 * 25 / (140) - 163 + 19 * 172 + 113 - 160 + 168 / 137 * 56 - 28 / 139 + 66 * 108 + 152 * 26 * 117 * 165 + 127 - 64 * 30 / 138 - (48) * (20) * (120) - 58 - 156 - ((49)) + 80 + 0 - 20 * 105 / (42) - 85 - 124 / (34 * 17) * (((5 * 21 + 57 - 62) + 49 - 15 / 30 * 59 + (69 + 56))) + 78 * 136 / 85 * 142 + (167) / 42 * 92 * (6) + 64 / 150 - 64 + 16 / 132 - 65 * 36 - 57 * (107) + 24 + 83 + 141 / 124 - 89 - 64 - 0 * 53 / (113 * 98) * (83 * 74 * (168) / 41 / 153 - 123 - 28 + 16 + 11 * 71 * 11 * 100 - 37 * 63 + 165) / (53 - 15) / 49 + 173 * 155 * 58 - 16 + 57 - 19 - 42 * (48) * 83 * 43 * 101 - 99 * 43 / 86 - 173 - 113 - 29 * 145 + 56 + 58 + 64 - 150 + 31 / 75 / 70 * 68 * (138) / (54) + (122 * 153) + (5) + (114) / 127 + 63 - (32) * 87 - 165 + 74 * 135 + 68 / 19 - (139) + 69 - 63 / 127 + 61 + (78 - 157)=-648930118=-648930118
-1 - 1/0=0=0
Error while evaluating: "1/0" - Cannot divide by zero
-1 - (=0=0
-1 - )=0=0
-1 - *=0=0
-1 - /=0=0
-1 - +=0=0
-1 - -=0=0
-1 - */+-=0=0
DONE 29 tests passed out of 29

Example Usage:

There is a sample program included in ./src/ called example_usage.c which can be compiled and run with

make example

The sample program shows how to use the eval() function to evaluate a string. Read the Makefile to learn how to build it.

License

This work is licensed under the GNU General Public License version 3 (GPLv3).