Relativistic Effects Calculator, Almost working

So I recently took on the task of making a 'Relativity Calculator' and am Having a trouble with some if statements. I am fairly new to programming, so forgive me if it's obvious. Here is the code.
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// This program is designed to tell a user the Relitivistic Length, mass and time
//of something going a certain speed under c
#include<iostream>
#include<math.h>
#include<stdlib.h>

using namespace std;

int main()
{

char choice;			 // User's choice
float c;			 //Speed of light
c = 299792458;

cout << "Welcome to Craig McRae's Relitivity Calculator!" << endl;
cout << "What would you like to calculate?" << endl;
cout << "A) Relitivistic Length, Mass and Time dilation" << endl;
cout << "B) Relitivistic Velocity addition" << endl;
cin >> choice;

if ( choice == A ) // here it says A is not defined
	{
	float V;			 //Speed
	float length, mass, time;	 //Initial mass, length, and time
	float Rlength, Rmass, Rtime; 	 //Relitivistic Length, mass and time
	float y;			 //Gamma or Lorentz transform

	cout << "How fast are you going? (m/s)";
	cin >> V;

	while   ( V >= c )
		{cout << "IMPOSSIBLE! NOTHING CAN GO THAT FAST!" << endl;
		cout << "How fast are you REALLY going? (m/s)";
		cin >> V;
		}

	cout << "How long were you traveling at this speed? (in seconds) ";
	cin >> time;
	
	cout << "Enter your mass in kg: ";
	cin >> mass;
	
	cout << "Enter your length in meters: ";
	cin >> length;
	
	y = sqrt(1 - ((V*V)/(c*c)));
	Rmass = mass / y;
	Rtime = time / y;
	Rlength = length * y;

	cout << "Traveling at a speed of " << V << "m/s, to an observer at rest you would appear to have a length of " << Rlength << " meters, a mass of " << Rmass << " kg, and " << time << " seconds for you would be " << Rtime << " seconds for the observer!" << endl;
	}

if ( choice == B ) // here it says B is not defined
	{
	float V1, V2, Vf;	//Velocities
	char ans;
	cout << "What is the first velocity?";
	cin >> V1;
	cout << "What is the second Velocity?";
	cin >> V2;
	cout << "Are they going in the same direction? (Y/N)";
	cin >> ans;
	if ( ans == Y) // here it says Y is not defined
		V2 = -1 * V2;
	
	//Calculations
	Vf = abs(V1 + V2);
	V2 = -1 * V2;
	Vf = Vf/(1 + (V1*V2)/(c*c));
	cout << " " << endl;
	cout << Vf << endl; //I incomplete final cout statement for testing

	}
return 0;
}

My problem is that it says A, B, and Y are not defined, and theyre not, I have them set up so the user inputs them. But when I do put them in as char, The program compiles, but does nothing after i input A or B. Any help is appreciated!
The program compiles, but does nothing after i input A or B.

Have you tried making your input upper case?
No that did not work either, but I fixed the problem by assigning them all numerical values, Thanks
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