CSC300: Some common errors and advice [12/12]

A common problem is using < when you mean >.

In the bound of a loop this can cause big trouble!

For example, consider:

LOOP1:
int i = 1;
while (i > a.length) {
  i += 1;
}

and

LOOP2:
int i = 1;
while (i < a.length) {
  i += 1;
}

If a.length is 0 or 1, then the LOOP1 runs forever!

Another common issue that comes up is incrementing in the wrong place.

LOOP3:
int i = 1;
while (i < a.length) {
  if (a[i] == 5.0) {
    result += 1;
    i += 1;
  }
}

If a is length 2 or more, and a[1] != 5.0, then this is an infinite loop!

Sometimes your indentation can get messed up if you are typing for a while... To fix that, use Source > Format. That is, use the Format option on the Source menubar item.

A final common issue I will mention for now. Sometimes you may forget to put in the curly braces. This can be confusing!

LOOP4:
int i = 1;
while (i < a.length) 
  if (a[i] == 5.0) {
    result += 1;
  }
  i += 1;

LOOP4 looks okay, right?

But if you format, it will turn into this:

LOOP5:
int i = 1;
while (i < a.length) 
  if (a[i] == 5.0) {
    result += 1;
  }
i += 1;

LOOP5 is the same as LOOP4, but the indentation has changed. It makes it clear that i is being incremented outside the loop. To fix this, you need to add curly braces:

LOOP6:
int i = 1;
while (i < a.length) {
  if (a[i] == 5.0) {
    result += 1;
  }
  i += 1;
}

Hurrah! finally a correct loop!