When an Int Runs Out

Part of the First Circuits section of Coddy's Arduino journey. Lesson 12 of 22.

A variable is stored in a fixed number of bits, tiny on/off switches in the board's memory. On the Uno, an int has 16 bits, so it can only hold numbers from -32,768 to 32,767.

Go past the top and it does not grow: it wraps round to the bottom. 32,767 plus 1 becomes -32,768. This is called an overflow, and the sketch gives no warning.

For bigger numbers, use a type with more bits:

long big = 100000;           // -2,147,483,648 to 2,147,483,647
unsigned long huge = 3000000000;  // 0 to 4,294,967,295

long has 32 bits. unsigned long has 32 bits but no negative numbers, so it goes twice as high: good for counts and times.

A long takes twice the memory of an int, and the Uno has only 2048 bytes for variables, so use int when the numbers stay small.

Challenge

Medium

The starter adds 1000 to count twenty times a second. Press Run and watch it turn negative after 32,000.

change the type of count so it can count past 100,000

Then Check.

Try it yourself

int count = 0;

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

void loop() {
  count = count + 1000;
  Serial.println(count);
  delay(50);
}

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in First Circuits

1Hello, Board

Blink an LED Setup and Loop Change the Blink Speed An LED of Your Own Two LEDs Taking Turns Comments in Your Sketch

4Decisions

Decisions with if Choosing with if and else Comparing Values Combining Conditions Read a Button

2Talking to Your Computer

Hello, Serial Monitor Print Versus Println Printing Numbers Your First Variable Counting UpWhen an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer Division Decimals with float A Blink That Speeds Up

Practice on your own: Arduino playground