C++实现简易的计算器，对简单的字符串求值

 

#include <iostream>
#include <string>
using namespace std;

class solution
{
public:
	int calculate(string s)
	{
		int result = 0, inter_res = 0, num = 0;
		char op = '+';
		char ch;
                //找到第一个不为空的字符
		for (int pos = s.find_first_not_of(' '); pos < s.size(); pos = s.find_first_not_of(' ', pos))
		{
			ch = s[pos];
                        //判断是否是数字
			if (ch >= '0' && ch <= '9')
			{
				int num = ch - '0';
                                //判断下一个字符是否也是数字
				while (++pos < s.size() && s[pos] >= '0' && s[pos] <= '9')
					num = num * 10 + s[pos] - '0';
				switch (op)
				{
				case '+':
					inter_res += num;
					break;
				case'-':
					inter_res -= num;
					break;
				case'*':
					inter_res *= num;