C++ 사칙연산계산기인데 오류가머인지모르겠습니다

/*
 * main.cpp
 *
 *  Created on: 2014. 11. 28.
 *      Author: 1407
 */
#include <iostream>
#include <ctype.h>
#include <stdlib.h>
#include <string.h>
#include <fstream>
using namespace std;
#define max 128
#define null 0
long stack[max];
double sstack[max];
int top = -1;
double ppush(double n)
{
	top++;
	if(top > max){
		cout <<" STACK OVERFLOW ! " << endl;
		exit(-1);
	}
	sstack[top] = n;
	return 1;
}
double ppop()
{
	if(top < 0)
		return -1;
	return sstack[top--];
}
long push(long n)
{
	top++;
	if(top > max){
	 cout << "STACK OVERFLOW !" << endl;
	 exit(-1);
	}
	stack[top] = n;
	return 1;
}
long pop()
{
	if(top < 0)
		return -1;
	return stack[top--];
}
int prior(int op)
{
	switch(op){
	case '(' : return 0;
	case '+' :
	case '-' : return 1;
	case '*' :
	case '/' : return 2;
	default : return 3;
	}
}
void postfix(char *postsik, char *sik)
{
	while(*sik !=null){
		if(*sik == '(') push(*sik++);
		else if(*sik == ')'){
			while(stack[top] != '('){
				*postsik++ = pop();
				*postsik++ = ' ';
			}
			pop(); sik++;
		}
		else if(strchr("+-*/",*sik) !=null){
			while(top >=0 && prior(stack[top]) >= prior(*sik)){
				*postsik++ = pop();
				*postsik++ = ' ';
			}
			push(*sik++);
		}
		else if(isdigit(*sik)){
			do{
				*postsik++ = *sik++;
			}
			while(isdigit(*sik) || *sik== '.');
			*postsik++=' ';
			}
		else
			sik++;
		}
	while(top >= 0){
		*postsik++ = pop();
		*postsik++ = ' ';
	}
	postsik--;
	*postsik = null;
}
double calc(double a, int n)
{
	int i;
	double x=a;
	//printf("---x=%f\n",x);
	for(i=0; i<n; i++) x=x/10;
	return x;
}
double post(char *p_sik)
{
	double jungsu, sosu,suja;
	int cnt;
	double i, j;
	while(*p_sik){
		if(isdigit(*p_sik)){
			jungsu = 0;
			do{
				jungsu = jungsu * 10+(*p_sik-'0');
				p_sik++;
			}
			while(isdigit(*p_sik));
			sosu=0; cnt=0;
			if(*p_sik=='.'){
				p_sik++;
				do{
					sosu=sosu*10+(*p_sik-'0');
					p_sik++; cnt++;
				}
				while(isdigit(*p_sik));
				sosu=calc(sosu,cnt);
			}
 
			suja=jungsu+sosu;
			ppush(suja);
		}
		else if(strchr("+-*/", *p_sik) !=null){
			i = ppop();
			j = ppop();
			switch(*p_sik){
				case '+' : ppush(j+i); break;
				case '-' : ppush(j-i); break;
				case '*' : ppush(j*i); break;
				case '/' : ppush(j/i); break;
			}
			p_sik++;
		}
		else
			p_sik++;
	}
	return pop();
}
int main()
{
	char postsik[max];
	char sik[max];
	cout << "산술식 입력 : ";
	gets(sik);
	postfix(postsik, sik);
	cout << "후위식 : " << postsik << endl;
	cout << "연산 결과 : " << post(postsik) << endl;
}