What does comma operator mean in a switch statement?

Question

I was given a question and was asked to give the output.

int main(void){  
    int x = 2;  
    switch(x){  
        case 1,2,1: printf(\"Case 1 is executed\         


        

Answer 1

You can not use twice the same 'case' value
This is not correct: case 1: case 2: case 1: printf("Case 1 is executed");
Tried to compile on VS2010 => (error C2196: case value '1' already used)