We've all been there:

Student: Teacher, I need help Teacher (comes over) Student (shows screen listing three bazillion errors)

The student has just written pages of code and finally decided to try to run it only to end up with pages of errors.

Error messages can at times be hard to read for beginners but to see and truth be told, they frequently don't even read them but over the years I've developed a practice that I've found helpful as a software developer and if students adopt the same practice it can save them a lot of time and effort.

The idea is very simple.

Compile and test one concept at a time.

It might seem silly, but if I'm writing a a program, my first compile might be code that looks like this:

  #include <iostream>

  using std::cout;
  using std::endl;

  int main()
  {
  
    return 0;
  }

or

  public class HelloWorld {

      public static void main(String[] args){
	
      }

  }

This might seem silly but it really doesn't take any effort. I have a key sequence to do this under Emacs and if I'm using an interactive language like Python or Clojure I just have to hit c-c c-c

This might seem silly but I do it out of muscle memory and it immediately tells me I don't have any syntax errors and my build system works.

Going further, I compile and test every time I code up what I call a concept. What's a concept? Let's look at some code. A student might write something like this to find prime number up to n:

def prime_list(n):
    for i in range(2,n):
        i_isPrime = True
        for j in range(i-1,1,-1):
            if i%j ==0 :
                i_isPrime = False
                break
        if i_isPrime:
            print(i)

There's a lot going on there. To me, a concept is

• A loop
• A complex calculation
• a conditional

All of these can have other concepts within.

In the above code, I'd probable write it as follows, adding in tests and print statements throughout the process:

def prime_list(n):
    for i in range(2,n):
        print(i)

def prime_list(n):
    for i in range(2,n):
        for j in range(i-1,1,-1):
            print(i,j)

def prime_list(n):
    for i in range(2,n):
        for j in range(i-1,1,-1):
            if i%j ==0 :
                print(i,"is not prime")
                break
        if i_isPrime:
            print(i)

def prime_list(n):
    for i in range(2,n):
        i_isPrime = True
        for j in range(i-1,1,-1):
            if i%j ==0 :
                i_isPrime = False
                break
        print(i,i_isPrime)
  

def prime_list(n):
    for i in range(2,n):
        i_isPrime = True
        for j in range(i-1,1,-1):
            if i%j ==0 :
                i_isPrime = False
                break
        if i_isPrime:
            print(i)