C++ Syntax

C++ Syntax Overview

C++ Compared to Python and Java

  • For comparison of programs side-by-side using functions, arrays / lists, and functions using C++, Python, and Java, see this page: C++ comparison

C++ and Other Languages

  • C++ are conceptually similar to other languages
    • Loops, functions, variables, etc. are in both
  • The biggest difference is the specific syntax is new
  • There are a few other things to note that we will discuss as we go

Example program

/* Awesome 
Photon 2 Program
*/
#include "OLED_screen.h"	//library

const int MAX_PRESSES = 4;	//globcal constant
int numPresses = 0;			//global variable
bool areDone = false;

void loop() {
  if (numPresses >= MAX_PRESSES) {
      areDone = true;
  }
}

Comments

  • // are single line comments
  • /* ... */are multiple line comments
/* Awesome 
Photon 2 Program
*/
#include "OLED_screen.h"	//library

Ending Lines

  • Every executable line of code ends with a semi-colon ;
int age = 4;
String animal = "cat";
  • Code blocks (e.g. loops, functions, ifs) do not end with semi-colons
void loop() {
  if (numPresses >= MAX_PRESSES) {
      areDone = true;
  }
}

Code Blocks

  • Blocks of code are started and ended with { }
  • Whitespace is doesn’t matter
void loop() {
  if (numPresses >= MAX_PRESSES) {
      areDone = true;
  }
}

void loop() {  if (numPresses >= MAX_PRESSES) {areDone = true;  }}

Both of the code blocks are correct and equivalent

Variables

type variableName = value

int numPresses = 0;
  • You must always specify the type of a variable when you declare it
  • Ex: int, double, String, bool

Constants

const type variableName = value;

const int MAX_PRESSES = 4;
  • const means the variable is a constant and cannot change after you initialize it

Aside: C++ Typing

  • Python and JavaScript are called weakly typed languages:
    • A variable can be hold a string, and then later hold an int
age = "Jurassic"
age = 34
  • C++ is called strongly typed language:
    • A variable must be declared as a type and cannot change
String age = "Jurassic";
age = 34		//Error!;

Functions: Return Values

returnType functionName (parameterType parameterName, ...) { ...}
  • Functions can may or may not return a value
  • Always specify the return type before the function name
double thisFunctionReturnsADouble() { ... }
  • void means the function does not return a value
void setup() { ... }

Functions: Input Parameters

returnType functionName (parameterType parameterName, ...) { ...}
  • Functions can may or may not take an input parameters
double squareRoot(int num) {...}
int sumNumbers(int num1, int num2) {...}
void loop() {...}

If Statements

Basic Syntax

if (condition){
  statement(s); //do this if condition is true
}

if (condition){
  statement(s); //do this if condition is true
} else {
  statement(s); //do this if false
}
  • Useful to execute code only under certain condition

Conditional Statement

  • Conditional statements are logical expressions that evaluate to true or false (think “yes” or “no”)
int x = 3, y = 10;
if (x == 2) {
    //this will be true because "x is equal to 3"
}
if (y != 10) {
    //this will NOT execute because 
}

While Loop Example

while (condition){
	statement(s);
}
  • Useful for code that repeats until a condition is true (especially if the number of iteration is unknown)
  • Though while loops are perfectly valid in C++, we will typically use for loops instead

For Loops

Basic Syntax

for (initialization; condition; update){
	statement(s);
}
  • Useful for code that repeats a set number of times
  • Uses a counter to control the loop

Basic Syntax

for (initialization; condition; update)
Initialization
  • Create and initialize variables only at the beginning of loop (ofter a counter)

Basic Syntax

for (initialization; condition; update)
Condition
  • Boolean expression that is checked at the end of each loop iteration.
  • Continue looping as long as this is true

Basic Syntax

for (initialization; condition; update)
Update
  • Increment (or decrement) your loop variables at the end of each loop iteration.

Example

for (int i = 0; i < 10; i++) {

__if (i % 2 == 0) {

____Serial.println(i);

Initialize variables

Example

for (int i = 0; i < 10; i++) {

__if (i % 2 == 0) {

____Serial.println(i);

Iteration #1: Check condition (even the first time)

  • If true, run loop
  • If false, exit loop

Example

for (int i = 0; i < 10; i++) {

__if (i % 2 == 0) {

____Serial.println(i);

Iteration #1: Run loop body (all the code in the loop)

Example

for (int i = 0; i < 10; i++) {

__if (i % 2 == 0) {

____Serial.println(i);

Iteration #1: Update the variable

Example

for (int i = 0; i < 10; i++) {

__if (i % 2 == 0) {

____Serial.println(i);

Iteration #2: Check condition again

  • If true, run loop
  • If false, exit loop

Resources on C++ Language

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