Question

I have a program I want to make which will ask to see whether a variable already exists. If it does, it displays it, if it does not, it creates it and stores it in the Arduino using the PROGMEM command. Can someone explain more about PROGMEM and how to make the program I’m talking about?

Answer 1

Generally speaking if you are creating any variables in functions they are existing only there when function is closed all variables are deleted. If you want to keep them alive try to create global variables or use static before it;
like here

static int myvariable;

And here is answer for your question

 if (myvariable!=NULL)
    {
     printfucntion(myvariable);
    }

solution for eeprom

EEPROM Read
Reads the value of each byte of the EEPROM and prints it to the computer.

#include <EEPROM.h>

// start reading from the first byte (address 0) of the EEPROM
int address = 0;
byte value;

void setup()
{
  Serial.begin(9600);
}

void loop()
{
  // read a byte from the current address of the EEPROM
  value = EEPROM.read(address);

  Serial.print(address);
  Serial.print("\t");
  Serial.print(value, DEC);
  Serial.println();

  //move to next address of the EEPROM
  address = address + 1;

  // there are only 512 bytes of EEPROM, from 0 to 511, so if you are
  // on address 512, wrap around to address 0
  // if you have arduinoMega probably there is more eeprom space
  if (address == 512)
    address = 0;

  delay(500);
}

I hope I helped.