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

is it a compiler error or not.

It will cause a compilation error (don't know about TURBO C++ but in modern compilers).
This is not the way switch statement works (invalid syntax in c/c++). You cannot reuse a case value in switch statement (see the link given by chris) The way you can do this;

 switch(x){
            case 1: case 2: case 3: printf("Case 1 is executed");
            break;
            default : printf("Default case us execyted"); 
          }