How do I resolve compiler error with my multi-lined macro in C

Let us look at the following plain multi-lined and multi-statement macro.

#define SAY_HELLO() \
                        printf("Hi, There!\n"); \
                        printf("Nice to meet you\n");

If you use the above macro as shown below, you will encounter compilation errors.

  if(manager)
    SAY_HELLO();
  else
    printf("You are not my manager..Why should I care?\n");

The above code expands to the following and results in compilation error as “else” part of the code is detached from the actual “if” condition.

  if(manager)
                   printf("Hi, There!\n");
                   printf("Nice to meet you\n");
  else
    printf("You are not my manager..Why should I care?\n");

If you attempt to wrap all the statements of macro in {…}, general usage of the macro will throw an error.

#define SAY_HELLO() \
                       { printf("Hi, There!\n"); \
                        printf("Nice to meet you\n"); }

General usage of the macro as shown below

   SAY_HELLO();

will expand to

{ printf("Hi, There!\n");
                        printf("Nice to meet you\n"); };

and results in compilation error again.

To resolve this problem, it is advised to use a dummy loop “do {…} while(0)” around all the statements as shown below.

#define SAY_HELLO() \
                       do { \
                         printf("Hi, There!\n"); \
                         printf("Nice to meet you\n"); \
                       } while(0)

This will ensure that no compilation error occurs with any type of usage of the macro.