计算器的改良

$Sample$Sample $Input$Input

6a-5+1=2-2a

$Sample$Sample $Output$Output

a=0.750

$Train$Train $of$of $Thought$Thought

一元二次方程
最后可以化成$kx + b = 0$kx+b=0
再化简可得$x = -\frac{b}{k}$x=−kb​
所以只需要求出$b$b(将常数相加，等号右边的要$*-1$∗−1)
和$k$k(将未知数的系数相加，等号右边同上)

#include<algorithm>
#include<iostream>
#include<cstring>
#include<cstdio>
using namespace std;
int n, m, l = 1, k, t = 1, tot;
char s, a;
int main()
{
	while(cin>>s)
	{
		if(s == '+')m += t * k * l, l = 1, tot = 0, k = 0;
		if(s == '-')m += t * k * l, l = -1, tot = 0, k = 0;
		if(s == '=')m += t * k * l, t = -1, tot = 0, k = 0, l = 1;
		if(s >= '0' && s <= '9')
		{
			k = k * 10 + s - '0', tot = 1;
		}
		if(s >= 'a' && s <= 'z')
		{
			a = s;
			if(tot)n += t * k * l;
			else n += l * t;
			k = 0, tot = 1;
		}
	}
	m += t * k * l;
	double ans = double(-m * 1.0 / n);
	if (ans == -0.0) ans = 0;
	printf("%c=%.3f", a, ans);
	return 0;
}