From: short <>
Date: Mon, 9 Jul 2001 23:03:00 +0000 (+0000)
Subject: Expression evaluation
X-Git-Tag: rh71~80
X-Git-Url: https://git.jankratochvil.net/?p=nethome.git;a=commitdiff_plain;h=72e178bb813f10de7c23fb988564607292bec4e9;hp=c516a4d7f9783bba3b20adb4e5807fd94912c4db

Expression evaluation
---

diff --git a/src/ev.c b/src/ev.c
new file mode 100644
index 0000000..f8f8d95
--- /dev/null
+++ b/src/ev.c
@@ -0,0 +1,130 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <ctype.h>
+#include <assert.h>
+
+#define BUFSIZE 100
+
+char *arg;
+
+int istack[BUFSIZE];
+char opstack[BUFSIZE];
+int istackp,opstackp;
+
+static char lex(int *ip)
+{
+char c;
+long l;
+
+	while (isspace(*arg)) arg++;
+	switch (*arg) {
+		case 0: case '+': case '-': case '*': case '/': case '(': case ')':
+			c=*arg;
+			if (c) arg++;
+			return(c);
+		case '0' ... '9':
+			l=strtol(arg,&arg,10);
+			*ip=l;
+			return 'n';
+		default:
+			fprintf(stderr,"Invalid characted in string: %s\n",arg);
+			exit(EXIT_FAILURE);
+		}
+}
+
+static int oppri(char op)
+{
+	switch (op) {
+		case 0: return(0);
+		case '+': case '-': return (10);
+		case '*': case '/': return (20);
+		case '(': return (2);
+		case ')': return (5);
+		default: assert(0);
+		}
+}
+
+static void evalit(void)
+{
+	assert(opstackp);
+	if (istackp<2) {
+		fprintf(stderr,"2 arguments for operator required!\n");
+		exit(EXIT_FAILURE);
+		}
+	istackp--;
+	switch (opstack[--opstackp]) {
+		case '+': istack[istackp-1]+=istack[istackp]; break;
+		case '-': istack[istackp-1]-=istack[istackp]; break;
+		case '*': istack[istackp-1]*=istack[istackp]; break;
+		case '/': 
+			if (!istack[istackp]) {
+				fprintf(stderr,"Division of %d by zero not supported!\n",istack[istackp-1]);
+				exit(EXIT_FAILURE);
+				}
+			istack[istackp-1]/=istack[istackp];
+			break;
+		}
+}
+
+static void pushop(char op)
+{
+int mypri=oppri(op);
+	while (opstackp && op!='(' && oppri(opstack[opstackp-1])>=mypri)
+		evalit();
+	if (!op) return;
+	if (op==')') {
+		if (!opstackp || opstack[opstackp-1]!='(') {
+			fprintf(stderr,"Not enough content for brackets-inside space!\n");
+			exit(EXIT_FAILURE);
+			}
+		opstackp--;
+		return;
+		}
+	assert(opstackp<BUFSIZE);
+	opstack[opstackp++]=op;
+}
+
+static void process(void)
+{
+char lastop=0,op;
+int curi;
+
+	istackp=opstackp=0;
+	for (;;) switch ((op=lex(&curi))) {
+		case 'n':
+			if (lastop=='n') {
+				fprintf(stderr,"Two successive numbers not permitted!\n");
+				exit(EXIT_FAILURE);
+				}
+			assert(istackp<BUFSIZE);
+			istack[istackp++]=curi;
+			break;
+		case '(':
+			if (lastop=='n') {
+				fprintf(stderr,"Open-bracket not permitted after number!\n");
+				exit(EXIT_FAILURE);
+				}
+			pushop(op);
+			break;
+		case '+': case '-': case '*': case '/': case ')': pushop(op); break;
+		case 0:
+			pushop(op);
+			if (istackp!=1||opstackp) {
+				fprintf(stderr,"Machine not in sane state on the end of expression, ints=%d,ops=%d!\n",istackp,opstackp);
+				exit(EXIT_FAILURE);
+				}
+			printf("%d\n",istack[0]);
+			return;
+		default: assert(0);
+		}
+}
+
+int main(int argc,char **argv)
+{
+int argn;
+	for (argn=1;argn<argc;argn++) {
+		arg=argv[argn];
+		process();
+		}
+	return(EXIT_SUCCESS);
+}