# V520\. Comma operator ',' in array index expression\.

The analyzer found a potential error that may be caused by a misprint\. An expression containing the ',' operator is used as an index for an array\.

Here is a sample of suspicious code:

```cpp
float **array_2D;
array_2D[getx() , gety()] = 0;
```

Most probably, it was meant to be:

```cpp
array_2D[ getx() ][ gety() ] = 0;
```

Such errors might appear if the programmer worked earlier with a programming language where array indexes are separated by commas\. 

Let's look at a sample of an error found by the analyzer in one project:

```cpp
float **m;
TextOutput &t = ...
...
t.printf("%10.5f, %10.5f, %10.5f,\n%10.5f, %10.5f, %10.5f,\n%10.5f, 
  %10.5f, %10.5f)",
    m[0, 0], m[0, 1], m[0, 2],
    m[1, 0], m[1, 1], m[1, 2],
    m[2, 0], m[2, 1], m[2, 2]);
```

Since the printf function of the TextOutput class works with a variable number of arguments, it cannot check whether pointers will be passed to it instead of values of the float type\. As a result, we will get rubbish displayed instead of matrix items' values\. This is the correct code:

```cpp
t.printf("%10.5f, %10.5f, %10.5f,\n%10.5f, %10.5f, %10.5f,\n%10.5f, 
  %10.5f, %10.5f)",
    m[0][0], m[0][1], m[0][2],
    m[1][0], m[1][1], m[1][2],
    m[2][0], m[2][1], m[2][2]);
```