1. Arduino Programming: “if” statements
Mechanical and Materials Engineering
Portland State University

2. Overview
Motivation: The need for conditional execution
“if” statement concepts
Logical expressions
Examples
On-line reference:

3. Use case: Making decisions in programs
Build a system to maintain water level in a tank

4. Use case: Making decisions in programs
Build a system to maintain water level in a tank
Arduino reads output from the level sensor
If water level is low, open the supply valve
An “if” statement is used to implement the decision

5. Logical statements control code execution
“if” construct to make a single choice “if – else” construct to choose either/or
if ( something is true ) {
code block }
if ( something is true ) {
code block 1
} else {
code block 2 }
See

6. Syntax of “if” construct
“if” construct to make a single choice “something is true” must be a logical expression Example:
if ( something is true ) {
code block }
Symbol
Meaning
<
Is less than
>
Is greater than ==
Is equal to
>=
Is greater than or equal to
<=
Is less than or equal to !=
Is not equal to
if ( x>0 ) {
y = sqrt(x); }

7. Test your understanding
What is the value of z? a.
x = 2;
y = 5;
z = 0;
if ( x < y ) {
z = y – x; } c.
x = 2;
y = 5;
z = 0;
if ( (y-x)<= 3 ) {
z = y/x; } b.
x = 2;
y = 5;
z = 0;
if ( x > y ) {
z = y – x; } d.
x = 2;
y = 5;
if ( (y-x)<= 3 ) {
z = y/x;
} else {
z = 0.0; }

8. Example: Night light int LED_pin = 12; void setup() {
pinMode(LED_pin, OUTPUT); }
void loop() {
int reading, sensor_pin=3, threshold = 150;
reading = analogRead(sensor_pin);
if ( reading < threshold ) {
digitalWrite(LED_pin, HIGH);
} else {
digitalWrite(LED_pin, LOW);

9. Example: Night light int LED_pin = 12; void setup() {
pinMode(LED_pin, OUTPUT); }
void loop() {
int reading, sensor_pin=3, threshold = 250;
reading = analogRead(sensor_pin);
if ( reading < threshold ) {
digitalWrite(LED_pin, HIGH);
} else {
digitalWrite(LED_pin, LOW);
analogRead returns
a value in the range
[0, 1023]

10. Compound “if-else-if”
Implement a piecewise function Notice the error-handling for x<x1 and x>x4
if ( x<x1 ) {
Serial.println(“Error: x<x1”);
} else if ( x<x2 ) {
y = ya;
} else if ( x<x3 ) {
y = yb;
} else if ( x<x4 ) {
y = yc;
} else {
Serial.println(“Error: x>x4”); }