Computer coding hw question

Question

1. What sort of runtime error will occur when this program is run?

void countdown () {

  int i = 100;

    int n = 5;

  while (i > 0) {

i = i -n;

n = n / -1;

print (i + n) ;

1. Divide by zero
2. Uninitialized memory read
3. Memory access violation
4. Infinite loop

(If someone could please help me understand this it would be very much appreciated, thanks!)

Answer 1

Look like you would get an infinite loop.

Even though the program is reducing i by n each time through the loop n is switching from positive to negative and back each time. The result is that i goes back and forth between two values (95, and 100) never getting close to the value that would stop the loop. The loop would alternately print 90 and 105.

One way to follow what is going on in a program like this is to create a table where each column represents some value that your are following and each row represents a point in time. After doing this a few times you should be able to picture this without the paper.

You would easily see in this case that the values repeat and the program is not going to make any progress.

Answer 2

It's an infinite loop....

Upon entering the while loop for the first time, i=100 and n=5

Then i=95 and n=-5

outputs 90

next iteration of while loop:

i becomes 95 - (-5) = 100 and n becomes 5

outputs 105

it is now in the same state as the first while loop;

so it will keep outputting 90 and 105 until you kill it

btw: you are missing TWO closing braces and your output statement should be

either printf("%d",i+5); or cout << i+5 << endl;

If you want to use printf then you must #include <stdio.h>; otherwise you must #include <iostream>