src/ev.c

   1 #include <stdio.h>
   2 #include <stdlib.h>
   3 #include <ctype.h>
   4 #include <assert.h>
   5
   6 #define BUFSIZE 100
   7
   8 char *arg;
   9
  10 int istack[BUFSIZE];
  11 char opstack[BUFSIZE];
  12 int istackp,opstackp;
  13
  14 static char lex(int *ip)
  15 {
  16 char c;
  17 long l;
  18
  19         while (isspace(*arg)) arg++;
  20         switch (*arg) {
  21                 case 0: case '+': case '-': case '*': case '/': case '(': case ')':
  22                         c=*arg;
  23                         if (c) arg++;
  24                         return(c);
  25                 case '0' ... '9':
  26                         l=strtol(arg,&arg,10);
  27                         *ip=l;
  28                         return 'n';
  29                 default:
  30                         fprintf(stderr,"Invalid characted in string: %s\n",arg);
  31                         exit(EXIT_FAILURE);
  32                 }
  33 }
  34
  35 static int oppri(char op)
  36 {
  37         switch (op) {
  38                 case 0: return(0);
  39                 case '+': case '-': return (10);
  40                 case '*': case '/': return (20);
  41                 case '(': return (2);
  42                 case ')': return (5);
  43                 default: assert(0);
  44                 }
  45 }
  46
  47 static void evalit(void)
  48 {
  49         assert(opstackp);
  50         if (istackp<2) {
  51                 fprintf(stderr,"2 arguments for operator required!\n");
  52                 exit(EXIT_FAILURE);
  53                 }
  54         istackp--;
  55         switch (opstack[--opstackp]) {
  56                 case '+': istack[istackp-1]+=istack[istackp]; break;
  57                 case '-': istack[istackp-1]-=istack[istackp]; break;
  58                 case '*': istack[istackp-1]*=istack[istackp]; break;
  59                 case '/':
  60                         if (!istack[istackp]) {
  61                                 fprintf(stderr,"Division of %d by zero not supported!\n",istack[istackp-1]);
  62                                 exit(EXIT_FAILURE);
  63                                 }
  64                         istack[istackp-1]/=istack[istackp];
  65                         break;
  66                 }
  67 }
  68
  69 static void pushop(char op)
  70 {
  71 int mypri=oppri(op);
  72         while (opstackp && op!='(' && oppri(opstack[opstackp-1])>=mypri)
  73                 evalit();
  74         if (!op) return;
  75         if (op==')') {
  76                 if (!opstackp || opstack[opstackp-1]!='(') {
  77                         fprintf(stderr,"Not enough content for brackets-inside space!\n");
  78                         exit(EXIT_FAILURE);
  79                         }
  80                 opstackp--;
  81                 return;
  82                 }
  83         assert(opstackp<BUFSIZE);
  84         opstack[opstackp++]=op;
  85 }
  86
  87 static void process(void)
  88 {
  89 char lastop=0,op;
  90 int curi;
  91
  92         istackp=opstackp=0;
  93         for (;;) switch ((op=lex(&curi))) {
  94                 case 'n':
  95                         if (lastop=='n') {
  96                                 fprintf(stderr,"Two successive numbers not permitted!\n");
  97                                 exit(EXIT_FAILURE);
  98                                 }
  99                         assert(istackp<BUFSIZE);
 100                         istack[istackp++]=curi;
 101                         break;
 102                 case '(':
 103                         if (lastop=='n') {
 104                                 fprintf(stderr,"Open-bracket not permitted after number!\n");
 105                                 exit(EXIT_FAILURE);
 106                                 }
 107                         pushop(op);
 108                         break;
 109                 case '+': case '-': case '*': case '/': case ')': pushop(op); break;
 110                 case 0:
 111                         pushop(op);
 112                         if (istackp!=1||opstackp) {
 113                                 fprintf(stderr,"Machine not in sane state on the end of expression, ints=%d,ops=%d!\n",istackp,opstackp);
 114                                 exit(EXIT_FAILURE);
 115                                 }
 116                         printf("%d\n",istack[0]);
 117                         return;
 118                 default: assert(0);
 119                 }
 120 }
 121
 122 int main(int argc,char **argv)
 123 {
 124 int argn;
 125         for (argn=1;argn<argc;argn++) {
 126                 arg=argv[argn];
 127                 process();
 128                 }
 129         return(EXIT_SUCCESS);
 130 }