Equation (expression) parser with precedence?

Question

I\'ve developed an equation parser using a simple stack algorithm that will handle binary (+, -, |, &, *, /, etc) operators, unary (!) operators, and parenthesis.

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Answer 1

Another resource for precedence parsing is the Operator-precedence parser entry on Wikipedia. Covers Dijkstra's shunting yard algorithm, and a tree alternate algorithm, but more notably covers a really simple macro replacement algorithm that can be trivially implemented in front of any precedence ignorant parser:

#include 
int main(int argc, char *argv[]){
  printf("((((");
  for(int i=1;i!=argc;i++){
    if(argv[i] && !argv[i][1]){
      switch(argv[i]){
      case '^': printf(")^("); continue;
      case '*': printf("))*(("); continue;
      case '/': printf("))/(("); continue;
      case '+': printf(")))+((("); continue;
      case '-': printf(")))-((("); continue;
      }
    }
    printf("%s", argv[i]);
  }
  printf("))))\n");
  return 0;
}

Invoke it as:

$ cc -o parenthesise parenthesise.c
$ ./parenthesise a \* b + c ^ d / e
((((a))*((b)))+(((c)^(d))/((e))))

Which is awesome in its simplicity, and very understandable.