How to find out if the result of the code is runtime error

Question

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there two codes and the answers are both runtime error, could you explain me what are the hints which would tell us that the answer is a runtime error

a- what is What does the following method return when the input array is{ 1, 2, 3 }?

Java

public static int mystery(int[] array) {
 int i = 0;
 int count = 0;
 while (i <= array.length) {
 if (array[i] %2 == 0) { 
count++;
}
 i++;
} 
return count;
}

the second one is :What String does the following code return if the input to the method is the String with contents ABCDE.

Java

public static String mystery(String input) { 
String tricky = ""; 
for (int i = 0; i < input.length(); i++) { 
tricky = tricky + input.charAt(i); 
i++; 
tricky = tricky + input.charAt(i);
} 
return tricky;
}

What I have tried:

(nothing)

Posted 5-Apr-18 5:46am

Member 13676546

Updated 5-Apr-18 7:53am

v4

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CPallini · Answer 1 · 2018-04-05T05:59:00

Solution 1

a) You know, array indices are zero-based (see, for instance Java Arrays[^]).

b) This is a beautiful example of ugly code. The lesson is: never mess up with with loop variables.

Posted 5-Apr-18 5:59am

CPallini

Updated 5-Apr-18 6:00am

v2

Dave Kreskowiak · Answer 2 · 2018-04-05T07:33:00

Solution 2

Quote:
what are the hints which would tell us that the answer is a runtime error

Knowing how each and every statement really works and "running" each line of code in your head.

That's about the only useful hint you can get on an assignment like this.

Posted 5-Apr-18 7:33am

Dave Kreskowiak

Patrice T · Answer 3 · 2018-04-05T07:54:00

Learn to indent properly your code, it show its structure and it helps reading and understanding. It also helps spotting structures mistakes.

C++

public static int mystery(int[] array) {
  int i = 0;
  int count = 0;
  while (i <= array.length) {
    if (array[i] %2 == 0) {
      count++;
    }
    i++;
  }
  return count;
}


public static String mystery(String input) {
  String tricky = "";
  for (int i = 0; i < input.length(); i++) {
    tricky = tricky + input.charAt(i);
    i++;
    tricky = tricky + input.charAt(i);
  }
  return tricky;
}

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