做一个运算器

表达式的计算（正确）

1.表达式的计算

主要考察栈的一些运用

先加减，后乘除，有括号先算，无需多讲；

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遇到数字入（收集数据）push_data,

（与运算符先比较优先级高入栈，低的话出栈运算并把数据入栈--

直到遇到比他高一级的运算符或者elem已空）最后push_elem,；；；

遇到‘（’入elem;   ')'那就将括号里面的运算

把剩下的做运算结果存入整型数组的第一个

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废话不多说，直接上代码！！！！

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#include <cstdio>
#include <cstdlib>
//#define _OJ_
//#define maxsize 100

typedef struct stack1
{
    char *elem;
    float  *data;
    int top;    int top1;
    int base;   int base1;
} stack1, *stack;

stack
creat_stack(void)
{
    stack s;
    s = (stack) malloc (sizeof(stack1));
    s->elem = (char*) malloc (100 * sizeof(char));
    s->data = (float*)  malloc  (100 * sizeof(float));
    s->top = s->base = 0;
    s->top1 = s->base1 = 0;
    return s;
}

float
data_pop(stack s)
{
    return s->data[--s->top];
}

char
elem_pop(stack s)
{
    return s->elem[--s->top1];
}

void
push_data(stack s, float x)
{
    s->data[s->top++] = x;
}

void
push_elem(stack s, char ch)
{
    s->elem[s->top1++] = ch;
}

int
data_isempty(stack s)
{
    if(s->top == s->base)
        return 1;
    else
        return 0;
}

int
elem_isempty(stack s)
{
    if(s->top1 == s->base1)
        return 1;
    else
        return 0;
}

char
gettop(stack s)
{
    return s->elem[s->top1 - 1];
}

float
gettop1(stack s)
{
    return s->data[s->top - 1];
}

float
operater(float a, char op, float b)
{
    switch (op) {
    case '+':  return a + b;
    case '-':  return a - b;
    case '*':  return a * b;
    case '/':  return a / b;
    }
}

int
get_rank(char op)
{
    switch (op) {
    case '+':
    case '-':  return 1;
    case '*':
    case '/':  return 2;
    case '(':  return 3;
    }

}

//建立一个字符数组和整型数组分别记录
int main(int argc, char const *argv[]) {
#ifndef _OJ_  //ONLINE_JUDGE
    freopen("input.txt", "r", stdin);
#endif

    char ch1;
    char str2[100];
    char  str[50];
    double  data2, data1, data, n, f;
    int    rank1, rank2, T, i = 0, j = 0, l1 = 0;
    stack s;

    scanf("%d", &T);
    while(T--){
    scanf("%s", str);
        i = 0;
        s = creat_stack();
      if(str[0] == '0' && str[1] == '')    break;//遇到零就结束
      if(str[0] != '0' && str[1] == '')    {printf("%c ", str[0]); continue;}
       //只有你一个数那么就输出
      while (str[i] != '=') {
          data = 0;    j = 0;
          for(l1 = 0;l1 < 50; l1++)
              str2[l1] = 0;

      if ('0' <= str[i] && str[i] <= '9') {
        while(('0' <= str[i] && str[i] <= '9') || (str[i] == '.')) {
            str2[j++] = str[i];
            i++;
      }
      f = atof(str2);//将数值以字符型存入一个数组里面，用atof将其转化为浮点数
      push_data(s,f);//收集数据传入data数组
      continue;
  }

      else if(str[i] == '(')
        push_elem(s,str[i]);
      else if(str[i] == ')')  {//遇右括号就把里面的数计算入栈
           while (gettop(s) != '(')  {
           data1 = data_pop(s);    data2 = data_pop(s);
           ch1   = elem_pop(s);
            n = operater(data2,ch1,data1);
            push_data(s,n);
        }
           elem_pop(s);
    }

     else{
        if(elem_isempty(s))    push_elem(s,str[i]);//先判断栈是否为空空的就入栈
        else {
            ch1 = gettop(s);    rank1 = get_rank(ch1);
            rank2 = get_rank(str[i]);
            while ((ch1 != '(') && (rank2 <= rank1) && elem_isempty(s) != 1) {
             ch1 = gettop(s);
             if(ch1 == '(') break;//注意不可和（作比较

             data1 = data_pop(s);    data2 = data_pop(s);
             ch1 = elem_pop(s);
             n = operater(data2,ch1,data1);
             push_data(s,n);
            }//把优先级别高的和相等的计算入栈
            push_elem(s,str[i]);
    }
}

           i++;
}
//把剩下的做运算结果存入整型数组的第一个
   while (!elem_isempty(s)) {
      data1 = data_pop(s);    data2 = data_pop(s);
      ch1   = elem_pop(s);
      n = operater(data2,ch1,data1);
      push_data(s,n);
    }


      int f1;
      f1 = int(gettop1(s));
      if(f1 == gettop1(s))
          printf("%d ", f1);
         else
              printf("%.2lf ", gettop1(s));
              // 利用其原理可以做一个计算器,如果计算之结果是整数就输出整数
                // 否则就输出浮点数
}
// printf("%d ", '');
    return 0;
}
// 1.000+2/4=
// ((1+2)*5+1)/4=