Why does my output says 'nan'?

Question

I typed an output to find the determinent of a quadratic equation
But the problem is that whenever I run the program and input the numbers the output says 'nan'
This is the program:
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
float a,b,c,d,e;
cout<<"enter 3 numbers";
cin>>a>>b>>c;
d=b*b-4*a*c;
e=d;
cout<<sqrt(e);
}

Answer 1

nan stands for not a number.
If the value of d is negative, then the output will be square root of negative number which is imaginary. In that case it'll print "nan"

Answer 2

use complex.h (might be called ccomplex for C++ but I am not sure), they provide complex operations and numbers

Answer 3

You can use a simple if statement to check if e is less than zero (OR greater than or equal to zero). Then output something else or perform some other code if e is negative.

A few examples:

if(e < 0) {
cout << "Number is negative. Please try again." << endl;
} else {
cout<<sqrt(e);
}

if(e < 0) {
e = e * -1; // make e positive
}
cout<<sqrt(e);

if(e > 0) {
cout<<sqrt(e);
} else {
// do something here
}
// or here

Answer 4

So how to get an output even if it is negative
Any help would be much appreciated