Generally, the solution is to avoid writing such code in the first place. The reason is that this:
Code:
int a = 1;2;3;
is the same as this except for formatting:
Code:
int a = 1;
2;
3;
That is, you have code that initialises a with 1, and then two lines that have no net effect.

The other thing is that for the expression (1,2,3), the comma operator is in use, which evaluates the left operand, then the right operand, with the result being the value of the right operand. Hence, you end up initialising b with 3. Sometimes this has some use when the left operand has a side effect, but in this case it doesn't so there's no point.