# V3081\. The 'X' counter is not used inside a nested loop\. Consider inspecting usage of 'Y' counter\.

The analyzer detected a possible error in two or more nested 'for' loops, when the counter of one of the loops is not used because of a typo\.

Consider the following synthetic example of incorrect code:

```cpp
for (int i = 0; i < N; i++)
  for (int j = 0; j < M; j++)
      sum += matrix[i, i];
```

The programmer wanted to process all the elements of a matrix and find their sum but made a mistake and wrote variable 'i' instead of 'j' when indexing into the matrix\.

Fixed version:

```cpp
for (int i = 0; i < N; i++)
  for (int j = 0; j < M; j++)
      sum += matrix[i, j];
```

Unlike diagnostics [V3014](https://pvs-studio.com/en/docs/warnings/v3014/), [V3015](https://pvs-studio.com/en/docs/warnings/v3015/), and [V3016](https://pvs-studio.com/en/docs/warnings/v3016/), this one deals with indexing errors only in loop bodies\.