cw自制计算器

#include <iostream>
#include <string>
using namespace std;
bool tt;
double calculate(string a) // 计算除去()的式子
{
	double x[1001];
	int y[1000]; // x存数字，y存运算符号
	bool t = false; // 接来下的数字是否为小数点后
	int t0 = 0; // 计算小数点后第几位
	for (int i = 0; i < 101; i++) // 初始化数组
	{
		x[i] = 0.0;
	}
	int yy = 0; // 计算运算符号个数
	for (int i = 0; i < (int)a.length(); i++)
	{
		if (a[i] == 43) // +
		{
			y[yy] = 1;
			yy++;
			t = false;
		}
		else if (a[i] == 45) // -
		{
			y[yy] = 2;
			yy++;
			t = false;
		}
		else if (a[i] == 42) // *
		{
			y[yy] = 3;
			yy++;
			t = false;
		}
		else if (a[i] == 47) // /
		{
			y[yy] = 4;
			yy++;
			t = false;
		}
		else if (a[i] == 46) // 小数点
		{
			t = true;
			t0 = 0; // 重置t0
		}
		else // 提取数字
		{
			if (t)
			{
				double u = (double)a[i] - 48;
				for (int k = 0; k <= t0; k++)
				{
					u /= 10;
				}
				x[i] += u;
				t0++;
			}
			else
			{
				x[yy] = x[yy] * 10 + a[i] - 48;
			}
		}
	}
	for (int i = 0; i < yy; i++) // 先算*和/
	{
		if (y[i] == 3)
		{
			x[i] = x[i] * x[i + 1];
			for (int k = i + 1; k < yy; k++)
			{
				y[k - 1] = y[k];
				x[k] = x[k + 1];
			}
			yy--;
			i--;
			continue;
		}
		else if (y[i] == 4)
		{
			if (x[i + 1] == 0)
			{
				tt = true;
				return 0.0;
			}
			x[i] = x[i] / x[i + 1];
			for (int k = i + 1; k < yy; k++)
			{
				y[k - 1] = y[k];
				x[k] = x[k + 1];
			}
			yy--;
			i--;
			continue;
		}
	}
	for (int i = 0; i < yy; i++) // 计算+和-
	{
		if (y[i] == 1)
		{
			x[i] = x[i] + x[i + 1];
			for (int k = i + 1; k < yy; k++)
			{
				y[k - 1] = y[k];
				x[k] = x[k + 1];
			}
			yy--;
			i--;
			continue;
		}
		if (y[i] == 2)
		{
			x[i] = x[i] - x[i + 1];
			for (int k = i + 1; k < yy; k++)
			{
				y[k - 1] = y[k];
				x[k] = x[k + 1];
			}
			yy--;
			i--;
			continue;
		}
	}
	return x[0];
}
int main()
{
	tt = false;
	cout << "C\t(\t)\t/\n\n7\t8\t9\t*\n\n4\t5\t6\t-\n\n1\t2\t3\t+\n\n \t0\t.\t=\n" << endl;
	cout << "欢迎使用cw自制计算器\n请输入宁要计算的式子：" << endl;
	string a;
	for (;a.find("=") == string::npos ; ) // 输入式子
	{
		string b;
		cin >> b;
		a = a + b;
	}
	if (a.find("=") != a.length() - 1) // =不在最后
	{
		cout << "数学错误！" << endl;
		return 0;
	}
	if (((a[0] > 41) && (a[0] < 48)) || ((a[a.length() - 2] > 41) && (a[a.length() - 2] < 48)))
	{
		cout << "数学错误！" << endl;
		return 0;
	}
	for (int i = 0; i < a.length() - 1; i++)
	{
		if (((((a[i] == 42) || (a[i] == 43)) || ((a[i] == 45) || (a[i] == 47))) || (a[i] == 40)) && ((a[i + 1] == 41) || (((a[i + 1] == 42) || (a[i + 1] == 43)) || ((a[i + 1] == 45) || (a[i + 1] == 47)))))
		{
			cout << "数学错误！" << endl;
			return 0;
		}
		if ((a[i] == 41) && (a[i + 1] == 40))
		{
			cout << "数学错误！" << endl;
			return 0;
		}
		if (((a[i] == 46) && (a[i + 1]) < 48) || ((a[i] < 48) && (a[i + 1] == 46)))
		{
			cout << "数学错误！" << endl;
			return 0;
		}
	}
	int pos = -1; // (位置
	a.erase(a.length() - 1); // 除去=
	for (; a.find('(') != string::npos; ) // 运算括号内内容
	{
		if (a.find(')', pos + 1) == string::npos)
		{
			cout << "数学错误！" << endl;
			return 0;
		}
		if (a.find('(', pos + 1) < a.find(')', pos + 1))
		{
			pos = a.find('(', pos + 1);
		}
		else
		{
			if (pos == -1)
			{
				cout << "数学错误！" << endl;
				return 0;
			}
			double r = calculate(a.substr(pos + 1, a.find(')', pos + 1) - pos - 1));
			string q = a.substr(0, pos);
			string w = a.substr(a.find(')', pos + 1) + 1);
			a = q + to_string(r) + w;
			pos = -1;
		}
	}
	if (a.find(')') != string::npos)
	{
		cout << "数学错误！" << endl;
		return 0;
	}
	double r = calculate(a); // 没有括号时运算式子
	if (tt) // 数学错误
	{
		cout << "数学错误！" << endl;
		return 0;
	}
	if (r - (int)r == 0)
	{
		cout << (int)r;
	}
	else
	{
		cout << r;
	}
}