I'm trying to find a good way to print leading 0, such as 01001 for a ZIP Code. While the number would be stored as 1001, what is a good way to do it?
I thought of using either case statements or if to figure out how many digits the number is and then convert it to an char array with extra 0's for printing, but I can't help but think there may be a way to do this with the printf format syntax that is eluding me.
printf("%05d", zipCode);
The 0 indicates what you are padding with and the 5 shows the width of the integer number.
Example 1: If you use "%02d" (useful for dates) this would only pad zeros for numbers in the ones column. E.g., 06 instead of 6.
Example 2: "%03d" would pad 2 zeros for one number in the ones column and pad 1 zero for a number in the tens column. E.g., number 7 padded to 007 and number 17 padded to 017.
If you are on a *nix machine:
man 3 printf
This will show a manual page, similar to:
0 The value should be zero padded. For d, i, o, u, x, X, a, A, e, E, f, F, g, and G conversions, the converted value is padded on the left with zeros rather than blanks. If the 0 and - flags both appear, the 0 flag is ignored. If a precision is given with a numeric conversion (d, i, o, u, x, and X), the 0 flag is ignored. For other conversions, the behavior is undefined.
Even though the question is for C, this page may be of aid.
ZIP Code is a highly localised field, and many countries have characters in their postcodes, e.g., UK, Canada. Therefore, in this example, you should use a string / varchar field to store it if at any point you would be shipping or getting users, customers, clients, etc. from other countries.
However, in the general case, you should use the recommended answer (printf("%05d", number);).
There are two ways to output your number with leading zeroes:
Using the 0 flag and the width specifier:
int zipcode = 123;
printf("%05d\n", zipcode); // Outputs 00123
Using the precision specifier:
int zipcode = 123;
printf("%.5d\n", zipcode); // Outputs 00123
The difference between these is the handling of negative numbers:
printf("%05d\n", -123); // Outputs -0123 (pad to 5 characters)
printf("%.5d\n", -123); // Outputs -00123 (pad to 5 digits)
ZIP Codes are unlikely to be negative, so it should not matter.
Note however that ZIP Codes may actually contain letters and dashes, so they should be stored as strings. Including the leading zeroes in the string is straightforward so it solves your problem in a much simpler way.
Note that in both examples above, the 5 width or precision values can be specified as an int argument:
int width = 5;
printf("%0*d\n", width, 123); // Outputs 00123
printf("%.*d\n", width, 123); // Outputs 00123
There is one more trick to know: a precision of 0 causes no output for the value 0:
printf("|%0d|%0d|\n", 0, 1); // Outputs |0|1|
printf("|%.0d|%.0d|\n", 0, 1); // Outputs ||1|
More flexible.. Here's an example printing rows of right-justified numbers with fixed widths, and space-padding.
//---- Header
std::string getFmt ( int wid, long val )
{
char buf[64];
sprintf ( buf, "% *ld", wid, val );
return buf;
}
#define FMT (getFmt(8,x).c_str())
//---- Put to use
printf ( " COUNT USED FREE\n" );
printf ( "A: %s %s %s\n", FMT(C[0]), FMT(U[0]), FMT(F[0]) );
printf ( "B: %s %s %s\n", FMT(C[1]), FMT(U[1]), FMT(F[1]) );
printf ( "C: %s %s %s\n", FMT(C[2]), FMT(U[2]), FMT(F[2]) );
//-------- Output
COUNT USED FREE
A: 354 148523 3283
B: 54138259 12392759 200391
C: 91239 3281 61423
The function and macro are designed so the printfs are more readable.
