题目链接：表达式求值
该题以前做过但是WA了，今天终于把他解决了，各种悲剧啊，又是考虑不周到啊。。。。。。。。。。。。。。。。。。。
所以贴出来纪念一下，并作为一个警示
/****
ps:注意当遇到 ）时处理到遇到（之前
当一个符号进栈，判断之前的符号是否可以出栈，知道没有可出栈的
*/ #include <cstdio>
#include <cstring>
#include <cstdlib> using namespace std; bool judge_fuhao(char ch,char ch1)//ch1为将进栈
{
//printf("fuhao---->%c %c\n",ch,ch1);
if(ch == '(' )
return true;
else if(ch1 == '+' ||ch1 == '-')
{
return false;
}
else if(ch1 == '*' || ch1 == '/')
{
if(ch == '+' || ch == '-' )
return true;
else
return false;
}
} double judge_mtah(char ch,double y,double x)//运算
{
//printf("%c %lf %lf\n",ch,x,y);
switch(ch)
{
case '+':
return x + y; break;
case '-':
return x - y; break;
case '/':
return 1.0*x / y; break;
case '*':
return x * y; break;
}
} int main()
{
int T;
scanf("%d",&T);
char ch[1003];
char stack_ch[1003];
double stack_a[1003];
int stack_a_t = 0;
int stack_ch_t = 0; while(T--)
{
//freopen("2.txt","w",stdout);
scanf("%s",ch);
stack_a_t = 0;
stack_ch_t = 0;
int len = strlen(ch);
char ans[1005];
int ans_t = 0;
double tmp = 0;
int i;
double x,y,z;
for(i = 0; i < len; i++)
{
if(ch[i] == '+'|| ch[i]=='-'||ch[i]=='*'||ch[i]=='/'||ch[i]=='('||ch[i]=='=')
{
if(ans_t != 0)
{
tmp = atof(ans);
ans_t = 0;
ans[ans_t] = '\0';
stack_a[stack_a_t++] = tmp;
}
if(ch[i] != '=')
{
if(stack_ch_t == 0 || ch[i] == '(')
{
stack_ch[stack_ch_t++] = ch[i];
}
else
while(1)//+-*/进来
{
if(stack_ch_t-1 < 0 || judge_fuhao(stack_ch[stack_ch_t-1],ch[i])== true)
{
stack_ch[stack_ch_t++] = ch[i];
break;
}
else
{
x = stack_a[stack_a_t-1];
stack_a_t--;
y = stack_a[stack_a_t-1];
stack_a_t--;
z = judge_mtah(stack_ch[stack_ch_t-1],x,y);
stack_ch_t--;
stack_a[stack_a_t++] = z;
}
}
}
else if(ch[i] == '='){
{
if(stack_ch_t > 1 && judge_fuhao(stack_ch[stack_ch_t-2],stack_ch[stack_ch_t-1]) == true )
{
x = stack_a[stack_a_t-1];
stack_a_t--;
y = stack_a[stack_a_t-1];
stack_a_t--;
z = judge_mtah(stack_ch[stack_ch_t-1],x,y);
stack_ch_t--;
stack_a[stack_a_t++] = z; }
}
}
}
else if(ch[i] == ')')
{
if(ans_t != 0)
{
tmp = atof(ans);
ans_t = 0;
ans[ans_t] = '\0';
stack_a[stack_a_t++] = tmp;
} while(1)
{
if(stack_ch[stack_ch_t-1] == '(')
{
stack_ch_t--;
break;
}
else
{
x = stack_a[stack_a_t-1];
stack_a_t--;
y = stack_a[stack_a_t-1];
stack_a_t--;
z = judge_mtah(stack_ch[stack_ch_t-1],x,y);
stack_a[stack_a_t++] = z;
stack_ch_t--;
}
}
}
else
{
ans[ans_t++] = ch[i];
ans[ans_t] = '\0';
}
}
for(i = stack_ch_t-1; i >= 0; i--)
{
x = stack_a[stack_a_t-1];
stack_a_t--;
y = stack_a[stack_a_t-1];
stack_a_t--;
z = judge_mtah(stack_ch[i],x,y);
stack_a[stack_a_t++] = z;
}
printf("%0.2lf\n",stack_a[0]);
}
return 0;
}