K&M exercise 1-24

[deckoff8]

Hey guys. I was having some trouble with exercise 1-24 in the K&M. I asks for a program to check a C program for rudimentary syntax errors like unbalanced parentheses, brackets and braces. I know my current program doesnt work perfectly, because it will count something like (()) as an error. However, I was confused about something else. I usually get a "state2r" value of 1 even if I don't input anything. Like I can input "abc" and it'll return a state2r value of 1. I was wondering if someone could take a look at it, because I am stumped. Thanks a lot.

#include <stdio.h>
#define MAXLINE 1000
#define IN 1   /* IN is inside parantheses/brackets/braces, OUT is out*/
#define OUT 0

int getfile(char line[], int maxline);
void check(char oldline[]);
int state1, state1r, state1l,state2, state2r, state2l, state3, state3r, state3l;

int getline(char s[], int lim)
{

int i, c;
for(i=0;i<lim-1 && (c=getchar())!='\n' && c!=EOF;i++)
s[i]=c;

if (c=='\n'){
s[i]='\n';
i++;
}

s[i]='\0';
return i;
}


void check(char oldline[]){
extern int state1, state1r, state1l,state2, state2r, state2l, state3, state3r, state3l;
/* state1 is parenthees. 2 is brackets. 3 is braces. #r is if there is unbalanced right side   #l is if you have unbalanced left side */
int i;
state1= state1r= state2= state2r= state3= state3r=state1l=state2l=state3l = OUT;

for(i=0; oldline[i]!=EOF; i++){
if (oldline[i]=='(' && state1 == OUT)
state1 = IN;

    else if (oldline[i]=='(' && state1 == IN)
         state1l=IN;

if (oldline[i]==')' && state1 == IN)
         state1=OUT;

    else if (oldline[i]==')' && state1 == OUT)
         state1r=IN;

if (oldline[i]=='[' && state2 == OUT)
state2 = IN;

    else if (oldline[i]=='[' && state2 == IN)
         state2l=IN;

if (oldline[i]==']' && state2 == IN)
         state2=OUT;

    else if (oldline[i]==']' && state2 == OUT)
         state2r=IN;


if (oldline[i]=='{' && state3 == OUT)
state3 = IN;

    else if (oldline[i]=='{' && state3 == IN)
         state3l=IN;

if (oldline[i]=='}' && state3 == IN)
         state3=OUT;

    else if (oldline[i]=='}' && state3 == OUT)
         state3r=IN;
}
}

main(){
int i;
char line[MAXLINE];

while ((i=getline(line, MAXLINE))>0){
check(line);
printf("If you see a one following the phrase then you have an unbalanced error of that type\n");
printf("Unclosed paranthese %d Extra left paratheses %d Extra right paranthese %d\n", state1, state1l, state1r);
printf("Unclosed bracket %d Extra left bracket %d Extra right bracket %d\n", state2, state2l, state2r);
printf("Unclosed brace %d Extra left brace %d Extra right brace %d\n", state3, state3l, state3r);
}
return 0;
}

[CommonTater]

Lose the extern statement on line 28...
You may want to rethink your printf() logic on lines 79 to 82... that's going to display ever time through the loop.

Instead of using in and out (1 and 0) you might find your statewise logic more plausible if you increment and decrement... for example if you have 19 open braces you're looking for 19 closing braces... increment your counter when a brace opens, decrement it when it closes... thus anything but 0 at the end of the program is an error.