Thread: Pretty printting

Code:

/* multiplication table.c */
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
  int row, clm;

  /* winxp system call erase if othe OS */
  system("TITLE Multiplication Table");
  for (row = 1; row <= 12; row++)
  {
    for (clm = 1; clm  <= 12; clm++)
      printf("%4d", row * clm);
    printf("\n");
  }
  getchar();

  return(0);
}

wow much better. thank you.

Couple questions. Why was it necessary to inlcude the stdlib.h in order to format the ouput differently. I checked for the fucntions and there wasn't any you utilized.

The stdlib header defines several general operation functions and macros.

Macros:

NULL
EXIT_FAILURE
EXIT_SUCCESS
RAND_MAX
MB_CUR_MAX

Variables:

typedef size_t
typedef wchar_t
struct div_t
struct ldiv_t

Functions:

abort();
abs();
atexit();
atof();
atoi();
atol();
bsearch();
calloc();
div();
exit();
free();
getenv();
labs();
ldiv();
malloc();
mblen();
mbstowcs();
mbtowc();
qsort();
rand();
realloc();
srand();
strtod();
strtol();
strtoul();
system();
wcstombs();
wctomb();

Also I tried to format the output with a field width as well and I did not get the same ouput. My field width was 10 -15, i experimented randomly.
I ask this because I read your tutorial at Flashdada about solving problems, today actually and I knew what it was I needed to do to solve it, but I think I got the logic wrong.
So my question is how did you know the best width specifier would be 4. What is the logic behind it?

Also on your tutorial it is very good, however, I'm sure it is a typo, but there is no header file and sevreal include statements, you might want to check it out for others like myself who download it. Thanks again for all your help and indirect advice.



Okay never mind. I see the system call. Doesn't the compiler automatically include those header files necessary for system calls? kinda like

Code:

#include <stdio.h>

......
.......
set = sizeof(var)/* used and works without calling Ctype or string.h */
.......
.......

Originally posted by caroundw5h
wow much better. thank you.

Couple questions. Why was it necessary to inlcude the stdlib.h in order to format the ouput differently. I checked for the fucntions and there wasn't any you utilized.

The system() call needs stdlib.h

So my question is how did you know the best width specifier would be 4. What is the logic behind it?

12 * 12 = 144

3 digits + 1 for spacing I'll bet

Okay never mind. I see the system call. Doesn't the compiler automatically include those header files necessary for system calls? kinda like

Code:

#include <stdio.h>

......
.......
set = sizeof(var)/* used and works without calling Ctype or string.h */
.......
.......

sizeof() is technically an operator (like + - *), not a function call. It is not in any header. And no, the compiler doesn't automatically include headers for you.

Where did you get the idea it was part of ctype or string.h?

My bad. Thanks for clearing that up. But how come i was able to make the system calls without the stdlib.h?

> But how come i was able to make the system calls without the stdlib.h?
The compiler just invents prototypes for functions it does not know about, based on the first use of that function. This is refererred to as implicit declaration.

Some compilers can be made to warn when this happens, and I think C99 compilers will definitely warn you about it.

For many of the standard library functions, the implicit declaration is good enough to generate correct code which does what you want. Long term, lack of prototypes will eventually bite.

> I should really still declare a protoype first?
Yes.

Although you can get away with defining the function before you call it, this only works well in a single source file.

You can write multi-file programs without prototypes if you want, but mistakes are easy to make and hard to diagnose. This is one of the reasons why prototypes were put into the ANSI-C standard (K&R didn't have such things).

> Cause it seems like there are a lot of things you can do in C but really shouldn't.
Yes there are.