EEPROM read and write in Arduino - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this EEPROM write and read code?

Consider the following Arduino code that writes a value to EEPROM and then reads it back. What will be printed on the Serial Monitor?

Arduino

 #include <EEPROM.h>

void setup() {
  Serial.begin(9600);
  EEPROM.write(10, 123);
  int val = EEPROM.read(10);
  Serial.println(val);
}

void loop() {}

A 123

B 0

C 255

D Compilation error

💡 Hint

EEPROM.write stores a byte at the given address, and EEPROM.read retrieves it.

The code writes the value 123 to EEPROM address 10, then reads it back and prints it. So the output is 123.

❓ Predict Output

intermediate

What value is stored after this EEPROM update code?

This code uses EEPROM.update to write a value. What value will be stored at address 5 after running this code?

Arduino

 #include <EEPROM.h>

void setup() {
  EEPROM.write(5, 50);
  EEPROM.update(5, 50);
  EEPROM.update(5, 100);
}

void loop() {}

A 0

B 100

C 50

D Compilation error

💡 Hint

EEPROM.update only writes if the new value differs from the stored one.

Initially 50 is written. The first update writes 50 again, so no change. The second update writes 100, which is different, so EEPROM stores 100.

🔧 Debug

advanced

Why does this EEPROM read code print wrong values?

The code below tries to read an int from EEPROM but prints unexpected values. What is the main reason?

Arduino

 #include <EEPROM.h>

void setup() {
  Serial.begin(9600);
  int val = EEPROM.read(0) + (EEPROM.read(1) << 8);
  Serial.println(val);
}

void loop() {}

A EEPROM.read returns bytes, but int needs two bytes combined correctly

B EEPROM.read returns signed values causing wrong results

C The code should use EEPROM.get to read an int instead of manual byte combination

D EEPROM.read can only read one byte, so reading two addresses is invalid

💡 Hint

Think about how to read multi-byte data types from EEPROM safely.

EEPROM.read reads one byte at a time. Combining bytes manually can cause errors. EEPROM.get reads multi-byte types correctly and safely.

📝 Syntax

advanced

Which option causes a compilation error in EEPROM write code?

Which of these code snippets will cause a compilation error?

A EEPROM.write(10, 100);

B EEPROM.write(10, 'A');

C EEPROM.write(10, 0xFF);

D EEPROM.write(10, 256);

💡 Hint

EEPROM.write expects a byte value (0-255).

256 is out of byte range and causes a compilation error or warning. Other values are valid bytes.

🚀 Application

expert

How many bytes are written by this EEPROM.put call?

Given the struct and EEPROM.put code below, how many bytes are written to EEPROM?

Arduino

 #include <EEPROM.h>

struct Data {
  int a;
  byte b;
  float c;
};

void setup() {
  Data d = {100, 5, 3.14};
  EEPROM.put(20, d);
}

void loop() {}

A 7 bytes

B 9 bytes

C 8 bytes

D 10 bytes

💡 Hint

Consider the size of each data type on Arduino Uno (int=2 bytes, byte=1 byte, float=4 bytes).

int (2 bytes) + byte (1 byte) + float (4 bytes) = 7 bytes total.