给胖子的最简单的计算器四则运算

计算器四则

#include <iostream>

// 从左到右计算简单四则表达式，除数为0的话返回false
bool calc_exp(const char* exp, float& result);

int main() {
	float result;

	char exp[]="4-3+2*5+7/3";
	std::cout << "表达式: " << exp << std::endl;

	if (!calc_exp(exp, result)) {
		std::cout << "表达式非法\n";
		exit(-1);
	}
	else {
		std::cout << "结果: " << result << std::endl;
	}
	return 0;
}

bool calc_exp(const char* exp, float& result) {
	if (exp == NULL) {
		return false;
	}

	char op;
	float x, y;
	const char *p = exp;

	x = *p - '0';
	p++;
	for (; *p != '\0'; p++) {
		op = *p;
		p++;
		y = *p - '0';
		switch (op) {
			case '+':
				x = x + y;
				break;
			case '-':
				x = x - y;
				break;
			case '*':
				x = x * y;
				break;
			case '/':
				if (y == 0) {
					return false;
				}
				x = x / y;
				break;
			default:
				return false;
		}
	}

	result = x;
	return true;
}