[Solved] Panic Runtime Error index out of range [3] with length 3

Question

Let’s say that you pass the string XII to your function. That makes len(s) 3, which means that the body of your loop would (if the panic didn’t occur) execute 4 times (when i is 0, 1, 2 and 3 since your condition is i <= len(s).

On the iteration where i is 2 (i.e. it refers to the second I in XII, the last character), when the line

nextInt := romanNum[s[i+1]]

attempts to access the next character (i+1 will be 3) then it will be out of bounds. Remember, slices/arrays are 0 indexed. This is the reason for the panic.

It’s also worth nothing that if the panic did not occur when i was 2, then it would certainly occur during the next iteration where i is 3, since 3 is out of bounds for s, on the following line:

currentInt := romanNum[s[i]]

To fix the issue, you need to reconsider how you approach the condition of the loop. Using <= here is likely to cause you a problem. Also, within the body of the loop, you need to consider that when you’re looking at the last character in the string, there is not a next character, but your code just assumes that there is. Addressing both of these problems should help you overcome the issue.

Accepted Answer

Let’s say that you pass the string XII to your function. That makes len(s) 3, which means that the body of your loop would (if the panic didn’t occur) execute 4 times (when i is 0, 1, 2 and 3 since your condition is i <= len(s).

On the iteration where i is 2 (i.e. it refers to the second I in XII, the last character), when the line

nextInt := romanNum[s[i+1]]

attempts to access the next character (i+1 will be 3) then it will be out of bounds. Remember, slices/arrays are 0 indexed. This is the reason for the panic.

It’s also worth nothing that if the panic did not occur when i was 2, then it would certainly occur during the next iteration where i is 3, since 3 is out of bounds for s, on the following line:

currentInt := romanNum[s[i]]

To fix the issue, you need to reconsider how you approach the condition of the loop. Using <= here is likely to cause you a problem. Also, within the body of the loop, you need to consider that when you’re looking at the last character in the string, there is not a next character, but your code just assumes that there is. Addressing both of these problems should help you overcome the issue.