Postfix lab

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

int t, i, j, k, l, d, x, y, z;
char str[100000], str2[100000], str3[100000];

void do_it()
{
    puts("Enter your expression or press Any key to continue");
}

int isoperator(char ch)
{
    if (ch == '+' || ch == '-' || ch == '/' || ch == '^' || ch == '*') return 1;
    return 0;
}

void check()
{
    for (k = l - 1; ;k--)
    {
        if (str2[k] == ')' || str2[k] == '(') break;
        if (str2[k] == '.') continue;

        if ((str[j] == '-' || str[j] == '+' && ( (str2[k] == '*' || str2[k] == '/') || str2[k] == '^' )) || ( (str[j] == '*' || str[j] == '/') && str2[k] == '^'))
        {
            str3[d] = str2[k];
            d++;
            str2[k] = '.';
        }
    }
    str2[l] = str[j];
    l++;
}

void exodus()
{
    for (j = strlen(str2); j >= 0; j--)
    {
        if (isoperator(str2[j]))
        {
            str3[d] = str2[j];
            d++;
            str2[j] = '.';
        }
    }
    str3[d] = '\0';
}

int main()
{
    for (; ;)
    {
        do_it();
        gets(str);
        z = strcmp(str, "0");
        if (z == 0) break;

        d = 0, l = 1;
        str2[0] = ')';

        for (j = 0; str[j] != '\0'; j++)
        {
            if (str[j] == '(')
            {
                str2[l] = str[j];
                l++;
            }
            if (isalnum(str[j]))
            {
                str3[d] = str[j];
                d++;
            }

            if (isoperator(str[j])) check();

            if (str[j] == ')')
            {
                for (k = l - 1; str2[k] != '('; k--)
                {
                    if (str2[k] == '.') continue;
                    str3[d] = str2[k];
                    d++;
                    str2[k] = '.';
                }
            }
        }
        str2[l] = '\0';
        exodus();

        printf("%s\n", str3);
        puts("");
    }
    return 0;
}