用matlab实现解一元二次方程的代码

Question

想用if语句实现解一元二次方程，运算结果总是出错。个人认为是字符串与数字转化有问题，但是未能解决，求大神帮忙看看代码
代码：
fprintf('we design the equation as "ax^2+bx+c=d"\n')
a=input('Enter the number of a=','s');
b=input('Enter the number of b=','s');
c=input('Enter the number of c=','s');
d=input('Enter the number of d=','s');
A=num2str('a');
B=num2str('b');
C=num2str('c');
D=num2str('d');
det=B^2-4*A*C
if det disp('there is not real number to answer this equation')
elseif det==0
x=-B/(2*A)
disp('the answer is')
elseif det>0
x1=(-B+det)/(2*A)
x2=(-B-det)/(2*A)
else
disp('unknown wrong')
end

输入
we design the equation as "ax^2+bx+c=d"
Enter the number of a=1
Enter the number of b=2
Enter the number of c=1
Enter the number of d=0

输出
det =

  -28808

there is not real number to answer this equation

Answer 1

字符转数字错了，改成如下：
A=str2num(a);
B=str2num(b);
C=str2num(c);
D=str2num(d);