Decimals with float

Part of the First Circuits section of Coddy's Arduino journey. Lesson 16 of 22.

An int only holds whole numbers. For a number with a fraction, use float:

float price = 2.75;

Serial.println(price) prints two digits after the point, 2.75. Give it a second number to choose how many: Serial.println(price, 3) prints 2.750.

Watch out for whole numbers inside a formula. In price * (9 / 5), the 9 / 5 is worked out first, with two whole numbers, and gives 1. Write the formula so a float is part of each division: price * 9 / 5 works left to right, and price * 9 is already a decimal number.

Challenge

Easy

Turn a temperature into Fahrenheit:

make float celsius = 21.5;
work out celsius * 9 / 5 + 32 into a float called fahrenheit
print fahrenheit with 3 digits after the point

It should show 70.700. Press Run, then Check.

Try it yourself

void setup() {
  Serial.begin(9600);
  // make celsius, work out fahrenheit, print it with 3 decimals
}

void loop() {
}

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 Up When an Int Runs Out

3Math on the Board

Named Constants Arithmetic Operators Integer DivisionDecimals with floatA Blink That Speeds Up

Practice on your own: Arduino playground