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csyntaxswitch-statementcomma-operator

In c, can a switch statement have 2 arguments?

int main()
{
   switch(1,2)
   {
      case 1:printf("1");break;
      case 2:printf("2");break;
      default: printf("error");break;
   }
}

Is this valid in c?

I thought it shouldn't be , but when I compiled it , it shows no error and produces output 2.

Solution

  • Yes, this is valid, because in this case, the , is a comma operator.

    Quoting C11, chapter §6.5.17, Comma operator, (emphasis mine)

    The left operand of a comma operator is evaluated as a void expression; there is a sequence point between its evaluation and that of the right operand. Then the right operand is evaluated; the result has its type and value.

    This (evaluates and) discards the left operand and uses the value of the right (side) one. So, the above statement is basically the same as

    switch(2)

    Just to elaborate, it does not use two values, as you may have expected something like, switching on either 1 or 2.