Exercise 4.11. Modify getop so that it doesn't need to use ungetch. Hint: use an internal static variable.

Exercise 4.11. Modify getop so that it doesn't need to use ungetch. Hint: use an internal static variable.

I use ungetch as a static variable.

/* getop: get next character ot numeric operand */

int getop(char s[])

{

    int i, c;

    static int ungetch = 0; //the last symvol

    if(ungetch == 0)

        c = getch();

    else

    {

        c = ungetch;

        ungetch = 0;

    }

    while((s[0] = c) == ' ' || c == '\t')

        c = getch();

    s[1] = '\0';

    if(!isdigit(c) && c != '.' && c != '-') // not a number

        return c; 

    i = 0;

    if (c == '-')

    {

        if(isdigit(c = getch()) || c == '.')

            s[++i] = c; //negative numbers

        else

            {

                if(c != EOF)

                    ungetch = c;

                return '-';

            }

    }

    if(isdigit(c)) //collect integer part

        while(isdigit(s[++i] = c = getch()))

            ;

    if(c == '.') //collect fraction part

        while(isdigit(s[++i] = c = getch()))

            ;

    s[i] = '\0';

    if(c != EOF)

        ungetch = c;

    return NUMBER;

}