数据结构表达式求值。为什么8*5*3算出来是120，而8*5*4却是-96，想问一下哪里有问题?

Question

#include<iostream>
using namespace std;
typedef int Status;
#define MAXSIZE 100
typedef char ElemType;
typedef struct
{
    ElemType* base;
    ElemType* top;
    int stacksize;
}SqStack;
Status InitStack(SqStack& s)//初始化
{
    s.base = new ElemType[MAXSIZE];
    if (s.base == NULL)
        return -1;
    s.top = s.base;
    s.stacksize = MAXSIZE;
    return 0;
}
Status Push(SqStack& s, ElemType e)//入栈
{
    if (s.top == s.stacksize + s.base)
        return -1;
    *s.top = e;
    s.top++;
    return 0;
}
Status Pop(SqStack& s, ElemType& e)//出栈
{
    if (s.base == s.top)
        return -1;
    e = *(s.top - 1);
    s.top--;
    return 0;
}
ElemType GetTop(SqStack s)//取栈顶元素
{
    if (s.top != s.base) 
        return *(s.top - 1);
}
Status In(ElemType ch)//判断是否为运算符
{
    if (ch == '+' || ch == '-' || ch == '*' || ch == '/' || ch == '(' || ch == ')'||ch=='#')
        return 1;
    else
        return 0;
}
Status Precede(ElemType a, ElemType b)//比较符号优先级
{
    if (a == '#')
        if (b == '#')
            return '=';
        else
            return '<';
    if (a == '+' || a == '-')
        if (b == '*' || b == '/' || b == '(')
            return '<';
        else
            return '>';
    if (a == '*' || a == '/')
        if (b == '(')
            return '<';
        else
            return '>';
    if (a == '(')
        if (b == ')')
            return '=';
        else
            return '<';
    if (a == ')')
        return '>';
}
Status Operate(ElemType a, ElemType ch, ElemType b)//进行二元运算
{
    if (ch == '+')
        return a + b;
    if (ch == '-')
        return a - b;
    if (ch == '*')
        return a * b;
    if (ch == '/')
        return a / b;
}
int EvaluateExpression()
{
    SqStack OPND,OPTR;
    char ch,m;
    ElemType x, y;
    InitStack(OPND);
    InitStack(OPTR);
    Push(OPTR,'#');
    cin >> ch;
    while (ch != '#' || GetTop(OPTR) != '#')
    {
        if (In(ch)==0)
        {
            Push(OPND, ch-'0');
            cin >> ch;
        }
        else
            switch (Precede(GetTop(OPTR), ch))
            {
            case '<':
            {
                Push(OPTR, ch);
                cin >> ch;
                break;
            }
            case '>':
            {
                Pop(OPTR, m);
                Pop(OPND, y);
                Pop(OPND, x);
                Push(OPND, Operate(x, m, y));
                break;
            }
            case '=':
            {
                Pop(OPTR, m);
                cin >> ch;
                break;
            }
            }
    }
    return GetTop(OPND);
}
int main()
{
    cout << "输入表达式：" << endl;
    cout << "计算结果为：" << EvaluateExpression();
}

Answer 1

因为数据类型都是char型，取值范围是-128到127，853=120在取值范围内，所以没问题；但854=160，超过127，溢出了，就成为负数了。负数值等于160-256=-96