Is there a way to tell how many times a for loop will execute before running it?

I am taking an intro to java course and I am taking a practice quiz. These quizzes are not graded and do not count towards our grade so I thought I would post here.

Under normal circumstances, I would just copy the code and paste it into an IDE but I wanted to know if there is a way to think about this logically so I can figure out the answer. On real exams, we are not allowed to use eclipse or anything like that to figure out an answer and this question would take way too long to do it by hand and count how many times it goes through the for loop.

Here is the question:

How many times does the print statement in the for loop execute?

    for(int i = 0; i <347589; i++) {
       System.out.print("Give me coffee!");
    }

You can basically just take the upper bound of the for loop as an answer, which is 347,589 in this case. To arrive at this answer, consider a for loop with a much smaller bound:

for (int i=0; i < 5; ++i) {
    System.out.println("Give me coffee!");
}

By inspection, we can see that this loop will execute when:

i = 0
i = 1
i = 2
i = 3
i = 4

It won't execute when i = 5, because that fails the condition. So, it executes five times, which is the same as the upper bound of the for loop. We can extrapolate this to the loop in your problem to get 347,589 as the answer.

There is no general way to figure out how many times a while loop will execute before running it. This fact is known as the undecidability of the halting problem. For loops are just syntactic sugar for while loops, so this applies to for loops as well. The halting problem is the subject of a great many awesome books, among which Gödel, Escher and Bach by Douglas Hofstadter.

However, the for loop you give is extremely simple: it increases i until i no longer satisfies i < 347589. The variable i starts at 0 and increases one by one: i++ is equivalent to i = i + 1;. So i takes all the successive values: 0, 1, 2, 3, 4, ...,347588 and every time, the line System.out.println("Give me coffee!"); is executed.

Then i takes the value 347589 and no longer satisfies i < 347589, so the loop halts.

In total, "Give me coffee!" was printed 347589 times.

If you don't like the syntax for for loops, your code is equivalent to the following code using a while loop:

int i = 0;
while (i < 347589)
{
    System.out.print("Give me coffee!");
    i = i + 1;
}

As you have a simple for-loop that executes only one statement multiple times, you can simply count. You might know that the loop starts with i=0 with the first execution and adds 1 after each execution until the condition i<347589 is false. So:

i=0 -> once (1.)
i=1 -> twice (2.)
...
i=347588 -> 347589 times (347589.)
i=347589 -> loop stops.

so the print statement will be executed 347589 times.

Obviously, FOR loop is not Java specific question.

To understand FOR loop properly let's take an easy example. <br>

  for (int i = 0; i < 10; i++) {
     System.out.println(i); 
  }

This code will print all number from 0 to 10 (Excluding). <br>
So, the range 0-10 has 10 different values:<br>

 0
 1 
 2
 3 
 4 
 5 
 6 
 7 
 8 
 9

When i becomes 10 FOR loop statement (i<10) will not be satisfied and the loop will be broken. <br>

So, in you case "Give me coffee!" will be printed 347589 times with the same logic.

In the course they might just want to check your knowledge towards the coding basics. In these type of problems you should notice most importantly 4-5 things.

1- Starting point of index.

2- Ending point of index, also check whether that value in included or not.

3- Increment/Decrement of index, whether index is increased/ decreased by 1 or some other value or pattern.

4- Is their any break statement inside the loop, which will also indicate that loop will run till specific condition.

In the example you gave starting point is 0 and end point is 347589 (excluded) with increment of 1, so loop will run. 347589 - 0 + 1( 0 based index) = 347589 times.