How can a program be made to print the line number where an error occurs? Ans. The ANSI C standard includes a predefined macro named __LINE__ that can be used to insert the current source code line number in your program. This can be a very valuable macro when it comes to debugging your program and checking for logic errors. For instance, consider the following portion of code: int print_document(char* doc_name, int destination) { switch (destination) { case TO_FILE: print_to_file(doc_name); break; case TO_SCREEN: print_preview(doc_name); break; case TO_PRINTER: print_to_printer(doc_name); break; default: printf('Logic error on line number %d!\n', __LINE__); exit(1); } } If the function named print_document() is passed an erroneous argument for the destination parameter (something other than TO_FILE, TO_SCREEN, and TO_PRINTER), the default case in the switch statement traps this logic error and prints the line number in which it occurred. This capability can be a tremendous help when you are trying to debug your program and track down what could be a very bad logic error.