the problem says that comments may contain every symbol so, comments may contain *)
so, should take the *) as we like so it will match as good as we can, or should we take *) as we meet it in the text?

#include<stdio.h>

char ch;
int sem = 0;
char str[16] = "=+-*/0123456789";

int search(char c)
{
    int i;
    for(i = 0; i < 15; i++)
        if(c == str[i]) return 0;
    return 1;
}

void getChar()
{
    scanf("%c", &ch);
}

void comment()
{
    while(1)
    {
        getChar();
        while(ch == '*')
        {
            getChar();
            if(ch == ')') return;
        }
        if(feof(stdin)) { sem = 1; return; }
    }
}

void expr()
{
    while(ch != ')')
    {
        if(search(ch))
        {
            if(ch == ')') return;
            else if(ch == '(')
            {
                getChar();
                if(ch == '*') comment();
                else expr();
            }
            else sem = 1;
        }
        getChar();
        if(feof(stdin)) { sem = 1; return; }
    }
}

int main()
{
    do
    {
        getChar();
        if(feof(stdin)) break;
        if(ch == '(')
        {
            getChar();
            if(ch == '*')
            {
                comment();
            }
            else
                expr();

        }
        else if(ch == ')')
        {
            sem = 1;
            break;
        }
    }
    while(!feof(stdin));

    if(sem) printf("NO\n");
    else printf("YES\n");
    return 0;
}

Edited by author 09.07.2004 18:43

Try test:
(1+2+3
)

Your program will print NO, but true answer is YES.
You must control '\n'...
I had same problem...

Thank you for the test!!