表达式求值

//2333;

#include <stdio.h>
#include <ctype.h>
#include <stack>
using namespace std;
#define MAXN 1000+10

char buf[MAXN];
stack<char> op ;  //符号队列 ; 
stack<double> n ;

//得到操作符的优先级 
int getValue(char c)
{
    if('(' == c) return 0;
    if('+'== c || '-'== c) return 1;
    if('*'== c|| '/'== c) return 2;
}

double calc(double a, double b, char c)
{
    //printf("出栈操作: %f, %c, %f \n", a, c, b); 
    switch(c)
    {
        case '+': return a+b;
        case '-': return a-b;
        case '*': return a*b;
        case '/': return a/b;
    }
}
//操作符出栈, 即进行一次计算 
void pull()
{
    double a, b;
    if(n.size()> 1 && !op.empty())
    {
        b=n.top(); n.pop();
        a=n.top(); n.pop();
        n.push(calc(a, b, op.top())); //printf("%d: 出栈结果入栈！\n", n.size()); 
        op.pop();   //printf("符号: %d 数字: %d 出栈完毕! \n", op.size(), n.size());
    }
}
int main()
{
    int N, i;
    double d;
    char c;
    scanf("%d", &N);
    while(N--)
    {
        scanf("%s", buf); i=0;
        while(1)
        {
            if(isalnum(buf[i]))
            {
                sscanf(buf+i, "%lf", &d); 
                n.push(d);
                while(isalnum(buf[i]) || '.'== buf[i]) i++; 
            }
            
            c=buf[i++];
            if('=' == c || '\0' == c) break;
            if('('== c)
            {
                op.push(c);  //printf("入栈\n"); 
            }
            else if(')'== c)
            {
                while(!op.empty())
                {
                    if('('== op.top()){
                        op.pop(); break;
                    }
                    pull() ;
                }
            } 
            else
            {
                //注意先后顺序, 不为空才能进行 op.top() 操作; 
                while(!op.empty() && getValue(c) <= getValue(op.top())) pull();
                op.push(c); //printf("%d: 符号入栈: %c \n", op.size(), c);  
            }
        }
        
        while(!op.empty()) pull();
        printf("%.2lf\n", n.top());
        while(!n.empty()) n.pop();
    }
    return 0;
} 

带空格， 无括号;

#include <stdio.h>
int main(){
double s[200];
double num;
while (scanf("%lf",&num)!=EOF){
    int n=0;  s[n++]=num;  char c=getchar();
    if (num==0&&c=='\n'){break;}
    char x;
    while(true){
    scanf("%c %lf",&x,&num);
    switch(x){
        case'+':s[n++]=num;break;
        case'-':s[n++]=-num;break;
        case'*':s[n-1]*=num;break;
        case'/':s[n-1]/=num;break;}
    if (getchar()=='\n'){break;}}
    double sum=0;
    for (int i=0;i<n;i++){sum +=s[i];}
    printf("%.2lf\n",sum);}
return 0;}