Error Message ("error: 'AnalogPin' was not declared in this scope")

I am writing the code to take the derivative of a signal but when I go to verify it I get the following message:

"In function 'void loop()':
Derivative:29: error: 'Sensor_Data' was not declared in this scope
Sensor_Data = analogRead(AnalogPin);
^
Derivative:29: error: 'AnalogPin' was not declared in this scope
Sensor_Data = analogRead(AnalogPin);
^
Derivative:30: error: 'x' was not declared in this scope
x = Sensor_Data;
^
Derivative:31: error: 'Rate' was not declared in this scope
delay(Rate);
^
Derivative:33: error: 'y' was not declared in this scope
y = Sensor_Data;
^
Derivative:38: error: 'Derivative' was not declared in this scope
Derivative = (y - x)/(Rate_s)
^
Derivative:38: error: 'Rate_s' was not declared in this scope
Derivative = (y - x)/(Rate_s)
^
exit status 1
'Sensor_Data' was not declared in this scope"

I don't really know why I am getting this message and I checked to make sure each variable was spelled the correct way.

Here is my code:

void setup() 
{
  int AnalogPin = 0;  //The input to the sensor data.
  float Sensor_Data = 0.0000;
  int Rate = 1000;           //This is an arbitrary value to distinguish 
                             //the window size of the sensor data.
  float Rate_s = 1.00;       //This is the sample rate in seconds
  int C = 1000;              //Constant to change Rate into seconds
  float Derivative = 0.0000; 
  float x;
  float y;
  
  //Setup the switch controlling the machine. LOW implies that the
  //trigger has not been hit and that the machine should keep operating.
  //HIGH implies that the trigger has been hit and that the machine
  //should stop operating(or do a specific action such as record this 
  //moment in memory etc...)
  
  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);
}

void loop() 
{
  //Average Data first. The Due can sample at 100 kHz without any
  //tampering within the code. To sample at a higher rate, change
  //the analog.Read() function in the setup.
  
  Sensor_Data = analogRead(AnalogPin);
  x = Sensor_Data;
  delay(Rate);
  Sensor_Data = analogRead(AnalogPin);
  y = Sensor_Data;

  //Take the derivative by using the algebraic equation for slope
  //rise/run.

  Derivative = (y - x)/(Rate_s);
  
  //or instead multiply by a constant, c = 1000 for millisecond
  //delays or c = 100,000 for microsecond delays.
  
  Derivative = (y - x)/(Rate * C);

  //The trigger for this application is when the derivative of the RMS of 
  //the signal crosses 0. Here you can make the code do something when the
  //trigger is hit. Right now all it does it stop the machine.
  
  if(Derivative > 0)
    {
      digitalWrite(13, HIGH);
    }
}

(deleted)

You need to understand the concept of Scope. See the posting at the top of this Forum titled Useful Links. Inside that post, look for C++ Programming, and then look for What is Scope. That should help you understand the answer to your question.

Such a simple mistake, thanks for the quick replies! My code works now.