Question

I have understood the entire functionality of this program except the way it handles a nested comment input. The functionality of the State Star is unclear to me. What does c!='*' imply?

Suppose the input is haha /* hello /*world */, then after the first star if a slash comes, the control shifts to the PROGRAM state. however why is it accounting for c!='*'?

#include<stdio.h>
#include<conio.h>

void main()
{
enum{ /*Enum construct declares states */
    PROGRAM,
    SLASH,
    STAR,
    QUOTE,
    COMMENT,
    LITERAL
}state;

/* If state is quote then its either " or '*/

state = PROGRAM;

for(;;)
{
    int c = getchar();
    int quote = 0 ;

    switch(state) {
    case SLASH:
        /* Program text following a slash */
        if (c == '*') {
            state = COMMENT;
            break;
        }
        putchar('/');
        state = PROGRAM;

    case PROGRAM:
        /*Program Text*/
        if (c == '\''||c == '"') {
            state = QUOTE;
            quote = c;
            putchar(quote);
        }
        else if (c == '/')
            state = SLASH;
        else
            putchar(c);
        break;

    case COMMENT:
        /* Comment */
        if (c == '*')
            state = STAR;
        break;

    case STAR:
        /*Comment following a Star */
        if (c == '/')
            state = PROGRAM;
        else if (c != '*') {
            state = COMMENT;
            putchar(' ');
        }
        break;

    case QUOTE:
        /*Within a quote or a string */
        putchar(c);
        if (c == '\\')
            state = LITERAL;
        else if (c == quote)
            state = PROGRAM;
        break;

    case LITERAL:
        /*Within a literal having /*/
        putchar(c);
        state = QUOTE;
        break;
    }
}

printf("Can it handle this /* I wonder */");
getch();
}

Answer 1

It’s to cope with input like this:

blah /* comment **/ blah
                 ^

If you reverted to COMMENT at the point I’ve marked, then you wouldn’t be looking for the / in order to revert to PROGRAM. You need to stay in STAR.