Error in Resistor Ladder and Weight Sensor Combined Code

So I am trying to make the LED turn off for both pins when a 12V battery is turned on. It gives me these error messages, whats the problem?

Error messages:
C:\Users\Kenny\AppData\Local\Temp\build1c2ee7d7ad85eb6c5bd17aec6f423563.tmp/core\core.a(main.cpp.o): In function `main':

C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino/main.cpp:43: undefined reference to `setup'

C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino/main.cpp:46: undefined reference to `loop'

collect2.exe: error: ld returned 1 exit status

exit status 1
Error compiling for board Arduino/Genuino Uno.

int ledPin = 4; // LED connected to digital pin 4
int ignition_input = 5;   // pushbutton connected to digital pin 5
int weight_input = 6;
int val = 0;     // variable to store the read value

void resistor_setup()
{
  pinMode(ledPin, OUTPUT);      // sets the digital pin 13 as output
  pinMode(ignition_input, INPUT);      // sets the digital pin 7 as input
  pinMode(weight_input, INPUT);
}

bool is_ignition_active() {
 if (digitalRead(ignition_input) == HIGH) {
   return true; 
 }
 return false;
}

bool is_weight_active() {
 if (digitalRead(weight_input) == HIGH) {
   return true; 
 }
 return false;
}

void resistor_loop()
{
  val = digitalRead(ignition_input);   // read the input pin
  digitalWrite(ledPin, val);    // sets the LED to the button's value
}

void weight_loop()
{
  val = digitalRead(weight_input);   // read the input pin
  digitalWrite(ledPin, val);    // sets the LED to the button's value
}

Where is setup()?
Where is loop()?

Did you read the error messages?

And please don't cross-post.
Duplicate deleted.

I forgot to add to my main post that I am new(no formal training) to coding. This is for a school project and I’m learning as a I go. Thank you so much for the help, but I still don’t know what the first error is for?

Usually, you are going to be most interested in the first error message that you get. In this particular case, these are the only ones that you need to handle:

C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino/main.cpp:43: undefined reference to `setup'

C:\Program Files (x86)\Arduino\hardware\arduino\avr\cores\arduino/main.cpp:46: undefined reference to `loop'

Once you handle these, that message about function ‘main’ will go away.

However, you have made a very basic mistake that makes me think that you should try some Arduino tutorials and examples first.