Given the following code:

1 var myArray = [3,7,8];

2 var tot;

3 for (var i =0; i

Question

Given the following code:

1 var myArray = [3,7,8];

2 var tot;

3 for (var i =0; i < myArray.length; i=i+1) {

4  tot = tot + myArray[i];

5  avg = tot/i;

6 }

7 alert(avg);

Which lines of code will cause errors when you try to run the program? Choose all that apply.

BlackTom AI · Accepted Answer

Variables declared without an initial value are undefined in JavaScript, so using them in arithmetic yields invalid numeric results (NaN) rather than a useful sum. That is the key concept here.

Step-by-step reasoning with intermediate values:
- Line 1: var myArray = [3,7,8]; — This correctly creates an array; no error.
- Line 2: var tot; — This declares tot and its value is undefined. Declaration itself is valid.
- Enter loop (line 3): first iteration i = 0.
  - Line 4: tot = tot + myArray[i];
    - Substitute current values: tot is undefined, myArray[0] is 3, so this becomes undefined + 3.
    - In JavaScript undefined + 3 → NaN (Not-a-Number). This is not a thrown exception but produces an invalid numeric value that will propagate through further calculations. Therefore line 4 causes a runtime logic error (produces NaN) because tot was never initialized to 0.
  - Line 5: avg = tot/i;
    - After line 4 we already have tot = NaN. Now avg = NaN / 0 (because i is 0 on first iteration).
    - NaN divided by 0 remains NaN. Additionally, dividing by i while i can be 0 is logically wrong for computing an average (division by zero is undefined mathematically). So line 5 also causes a runtime problem and yields an incorrect result.
- Subsequent iterations will keep tot and avg as NaN, and alert(avg) will display NaN.

Why the other lines are not the cause:
- Line 1 is valid syntax and correctly initializes the array.
- Line 2 is a valid declaration; the issue arises because it is not initialized to 0, but the declaration itself does not cause an error.

Correcting the code would require initializing tot (for example, var tot = 0;) and computing avg after the loop using tot / myArray.length.

Conclusion: Lines 4 and 5 are the lines that cause runtime errors/incorrect results, matching the provided answer: 4 and 5.

Given the following code: 1 var myArray = [3,7,8]; 2 var tot; 3 for (var i =0; i < myArray.length; i=i+1) { 4 tot = tot + myArray[i]; 5 avg = tot/i; 6 } 7 alert(avg); Which lines of code will cause errors when you try to run the program? Choose all that apply. 多项选择题

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