Programming in C

390 Chapter 18 Debugging Programs

int main (void)

{

int i, j, k, nread;

nread = scanf ("%d %d %d", &i, &j, &k);

#ifdef DEBUG

fprintf (stderr, "Number of integers read = %i\n", nread);

fprintf (stderr, "i = %i, j = %i, k = %i\n", i, j, k);

#endif

printf ("%i\n", process (i, j, k));

return 0;

}

Program 18.1 Output

1 2 3

Number of integers read = 3

i = 1, j = 2, k = 3

6

Program 18.1 Output (Rerun)

1 2 e

Number of integers read = 2

i = 1, j = 2, k = 0

3

Note that the value displayed for kcan be anything because its value was not set by the

scanfcall and it was not initialized by the program.

The statements

#ifdef DEBUG

fprintf (stderr, "Number of integers read = %i\n", nread);

fprintf (stderr, "i = %d, j = %d, k = %d\n", i, j, k);

#endif

are analyzed by the preprocessor. If the identifier DEBUGhas been previously defined

(#ifdef DEBUG), the preprocessor sends the statements that follow up to the #endif(the

two fprintfs) to the compiler to be compiled. If DEBUGhasn’t been defined, the two

Program 18.1 Continued