HDU1237计算器模拟

计算器模拟
题目
1.中缀转为后缀
2.题目考察逆波兰表达式

注意事项:
增加括号用法
atoi_将string转为int: atoi(str.c_str())
换行
多位数字：往后遍历
stack: 没有clear用法swap ////// 清空的多种方法
string和intchar之间频繁转换是难点
string转int
将多位数字压栈处理

#include <iostream>
#include <stack>
#include <cstring>
#include <iomanip>


using namespace std;

stack<string> s1;
stack<char> s2;
stack<string> s3;

int getL(char a) {
	switch (a) {
		case '+': {
			return 4;
			break;
		}
		case '-': {
			return 4;
			break;
		}
		case '*': {
			return 5;
			break;
		}
		case '/': {
			return 5;
			break;
		}
		default:
			break;
	}
	return 0;
}

void g(char words[], int len) {
	stack<string>().swap(s1);
	stack<char>().swap(s2);
	string ts;
	for (int i = 0; i < len; ++i) {
		if (words[i] == ' ')
			continue;
		if (words[i] == '+' || words[i] == '-' || words[i] == '*' || words[i] == '/') {
			while (true) {
				if (s2.empty() || s2.top() == '(') {
					char t = words[i];
					s2.push(t);
					break;
				}
				int l = getL(words[i]);
				int la = getL(s2.top());
				if (l > la) {
					char t = words[i];
					s2.push(t);
					break;
				} else {
					string t;
					t.push_back(s2.top());
					s1.push(t);
					s2.pop();
				}
			}

		} else if ( words[i] >= '0' && words[i] <= '9') {//难点
			string t;
			t.push_back(words[i]);
			while (words[i + 1] >= '0' && words[i + 1] <= '9' ) {
				t.push_back(words[i + 1]);
				++i;
			}
			s1.push(t);
		} else {
			if (words[i] == '(') {

				s2.push(words[i]);
			} else {
				while (s2.top() != '(') {
					string t;
					t.push_back(s2.top());
					s1.push(t);
					s2.pop();
				}
				s2.pop();
			}
		}
	}
	while (!s2.empty()) {
		string t;
		t.push_back(s2.top());
		s1.push(t);
		s2.pop();
	}
	string Re;
	while (!s1.empty()) {
		Re = s1.top();
		s1.pop();
		s3.push(Re);
	}
}

int isop(string a) {
	if (a == "*" || a == "+" || a == "-" || a == "/")
		return 1;
	else
		return 0;
}

int main() {
	char words[1000];
	int len;
	stack<double> ans;
	string ch;
	while (gets(words)) {
		if (words[0] == '0' && strlen(words) == 1)
			break;
		len = strlen(words);
		g(words, len);
		int temp = s1.size();
		double a, b;
		while (!s3.empty()) {
			if (isop(s3.top())) {
				b = ans.top();
				ans.pop();
				a = ans.top();
				ans.pop();
				ch = s3.top();
				if (ch == "+") {
					a = a * 1.0 + b;
					ans.push(a);
				} else if (ch == "-") {
					a = a * 1.0 - b;
					ans.push(a);
				} else if (ch == "*") {
					a = a * 1.0 * b;
					ans.push(a);
				} else {
					a = a * 1.0 / b;
					ans.push(a);
				}
				s3.pop();
			} else {
				ch = s3.top();
				a = atoi(ch.c_str());
				ans.push(a);
				s3.pop();
			}
		}
		double outA = ans.top();
		cout << setiosflags(ios::fixed) << setprecision(2) << outA << endl;
		ans.pop();
	}
	return 0;
}