K&R Exercise 5-10, reverse polish notation evaluator, this is rough

kr5-10.c

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

int main(int argc, char *argv[])
{
    float polishStack[100];
    float *stackPtr;
    float tempx, tempy;
    float *start;
    stackPtr = polishStack;
    start = stackPtr;
    // don't really need this here, but i'll go with it
    *stackPtr++ = 0.0;
    *argv++;
    // so funny, * on arg is glob in bash, thanks
    // try \* to make it work
    while (--argc)
    {
        // check if first character of current argument
        // is punctuation (this includes math ops)
        // and that we won't underflow the stack
        if (ispunct(**argv) && (stackPtr-2) > start)
        {
            tempx = *--stackPtr;
            tempy = *--stackPtr;
            printf("%f %c %f\n", tempy, **argv, tempx);
            if (**argv == '+')
            {
                //pop off stack, push solution to stack
                *stackPtr++ = tempx + tempy;
            } else if (**argv == '-')
            {
                *stackPtr++ = tempy - tempx;
            } else if (**argv == '/')
            {
                *stackPtr++ = tempy/tempx;
            } else if (**argv == '*')
            {
                *stackPtr++ = tempx*tempy;
            } else {
                // no operator, push temp back
                *stackPtr++ = tempy;
                *stackPtr++ = tempx;
            }
            *argv++;
        }
        else if (isdigit(**argv))
        {
            *stackPtr++ = atof(*argv++);
        }
    }
    if (stackPtr-2 == start)
        printf("%f \n", *--stackPtr);
    else
        printf("Too many inputs\n");
    return 0;
}