表达式计算
输入表达式计算出值
#include <iostream>
#include <stack>
#include <algorithm>
#include <cmath>
using namespace std;
stack<int> nums;
stack<char> ops;
void cal()
{
int a = nums.top();
nums.pop();
int b = nums.top();
nums.pop();
char c = ops.top();
ops.pop();
int d = 0;
if (c == '+')
d = b + a;
else if (c == '-')
d = b - a;
else if (c == '*')
d = b * a;
else if (c == '/')
d = b / a;
else
d = pow(b, a); // ^
nums.push(d);
}
int main()
{
string str;
cin >> str;
string left;
for (int i = 0; i < str.size(); i++)
left += '(';
str = left + str + ')';
for (int i = 0; i < str.size(); i++)
{
if (isdigit(str[i]))
{
int j = i, t = 0;
while (isdigit(str[j]))
{
t = t * 10 + str[j] - '0';
j++;
}
nums.push(t);
i = j - 1;
}
else
{
char c = str[i];
if (c == '(')
ops.push(c);
else if (c == '+' || c == '-')
{
if (c == '-' && i && !(isdigit(str[i - 1])) && str[i - 1] != ')')
{
int j = i + 1, t = 0;
while (isdigit(str[j]))
{
t = t * 10 + str[j] - '0';
j++;
}
nums.push(-t);
i = j - 1;
}
else
{
while (ops.top() != '(')
cal();
ops.push(c);
}
}
else if (c == '*' || c == '/')
{
while (ops.top() == '*' || ops.top() == '/' || ops.top() == '^')
cal();
ops.push(c);
}
else if (c == '^')
{
while (ops.top() == '^')
cal();
ops.push(c);
}
else if (c == ')')
{
while (ops.top() != '(')
cal();
ops.pop();
}
else
cout << "invalid operator!" << endl;
}
}
cout << nums.top() << endl;
return 0;
}
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