External Resources

• printf reference
• Transitioning from python 2.x to C++ (thanks to CS35 profs)
• C++ Tutorial from w3schools
  • Note that many of the examples use cout output information; in Mbed we will instead be using printf or the serial monitor (pc.write)

C++ Crash Course

Major differences between Python or MATLAB and C++

• Programs are compiled and we can’t use an interpreter (command line type interface)
  • This means we have to run full programs rather than testing out individual lines of code
  • Good debugging practice is therefore really important, using print statements or the debugger
• Types are required!
  • A type needs to be used when creating a new variable or for the return value of a function
  • Common types: char, int, bool
• We need to declare variables and functions

  • Variables can be declared, initialized, and assigned

    • Declaring a variable might look like this: char myChar;. It reserves space for a character variable myChar but does not initialize it to any specific value.
    • Initializing a variable is a special word for assignment on declaration: char myChar = 'H';
    • Assignment uses the = operator to set a variable to a specific value: myChar = 'H';

  • Functions can be declared and defined

    • int addTwoInts (int a, int b); is an example of a function declaration. Notice how we have not said what the function does besides yet.

    • A function definition looks like this:

      int addTwoInts (int a, int b) {
      	return a + b;
      }
      

  • Our compiler reads code from top to bottom, so variables and functions need to be at least declared before they can be used. For convenience, we usually declare variables and functions at the top of files, unless they are declared in special files called header files (we’ll discuss this more in lecture 3).

• Syntax

  • C++ is not case sensitive or sensitive to white space (unlike python), and the syntax for things like loops or functions is a little different than for MATLAB. Brackets are used to separate different elements of code, and a semi colon ; is used at the end of most statements.

    if (a > b) {
    	printf("A is greater than B\\n");
    }
    

  • if statement syntax

    if (condition1) {
      // block of code to be executed if condition1 is true
    } else if (condition2) {
      // block of code to be executed if the condition1 is false and condition2 is true
    } else {
      // block of code to be executed if the condition1 is false and condition2 is false
    }
    

  • for loop syntax

    for (statement 1; statement 2; statement 3) {
      // code block to be executed
    }
    

    Statement 1 is executed (one time) before the execution of the code block.

    Statement 2 defines the condition for executing the code block.

    Statement 3 is executed (every time) after the code block has been executed.

    for (int i = 0; i < 5; i++) {
      printf("%d\\n",i);
    }
    

  • while loop syntax

    while (condition) {
      // code block to be executed
    }
    

  • Switch case syntax

    switch(expression) {
      case x:
        // code block
        break;
      case y:
        // code block
        break;
      default:
        // code block
    }
    

  • Comments

    • Comments in C++ can be either // for comments on a single line or between /* and */ for a multi-line comment.

    // Single line comment
    
    /* Multi-line comment
    
    ...
    ... */
    

Using Header (.h) and C++ files (.cpp)

Header (.h) files are commonly used alongside files with C++ code (.cpp) files. A header file includes information that would go at the top of your program if the program was in main.cpp. They are useful for keeping code organized.

What goes in a header file vs. C++ is a matter of convention, not a strict requirement. By convention:

• Header files contain only declarations of variables and functions, not definitions.
• C++ files contain only definitions of variables and functions.
• A header file’s name matches the name of the C++ file that it accompanies (if one exists).

Note that the header / C++ file pairing only applies for C++ files that are outside of main.cpp; if everything is in one file, you can put whatever would be in a header file at the top of the file (hence the name “header”). Header files also contain special directives to ensure that the declarations in the file are only included once per project (see below). The underscores around the header name are also a convention and not required.

Here’s an example header and C++ setup:

Example header file (add.h)