Using with atoi() in C

Question

I'm trying to use atoi() but I need the 0 in the front, but the function ignores it

  sprintf(str, "%d%d%d%d",comp[cont][0],comp[cont][1],comp[cont][2],comp[cont][3]);
  conv=atoi(str);  

  printf("%d \n",conv);

When I print str: 0100
And conv: 100
Is there any way to show the 0?

You can try using `printf` with a leading zero. http://stackoverflow.com/questions/153890/printing-leading-0s-in-c — austin, Dec 28 '13 at 16:39
The leading zero is not part of the *value*, it's part of the *representation*. — Oliver Charlesworth, Dec 28 '13 at 16:39
In C a leading `0` indicates the octal representation of an integer value: `020==0x10=16`. Binary valued I'd prefix with a `0b`. — alk, Dec 28 '13 at 17:01
`str` has a leading 0 if and only if `comp[cont][0]` is 0, so you want to print `conv` with a leading 0 if and only if `comp[cont][0]` was 0 at the time `str` was created but you do not want to output `str` itself? And, if yes, why? — mafso, Dec 28 '13 at 17:07
str is a char, I needed it to concatenate the 4 int, them using atoi() I converted it into an int again because I need to convert the binary to decimal — user3075022, Dec 28 '13 at 17:13

score 6 · Accepted Answer · answered Dec 28 '13 at 16:39

6

It's because integers simply doesn't have zeros in front of them.

You need to print it with that:

printf("%04d \n",conv);

You might find e.g. this printf reference useful.

answered Dec 28 '13 at 16:39

I know they dont, but it's a binary number and I need the zero to convert it to decimal and write it on a txt. It worked, thanks! – user3075022 Dec 28 '13 at 16:44

score 3 · Answer 2 · answered Dec 28 '13 at 16:39

3

Just change the printf format:

printf("%04d \n",conv);

answered Dec 28 '13 at 16:39

James M

score 1 · Answer 3 · answered Dec 28 '13 at 16:40

1

Just append the zero while printing. Try the following

print("0%d\n", conv);

answered Dec 28 '13 at 16:40

doptimusprime

It will fail when you have 0010 – Digital_Reality Dec 28 '13 at 16:41
1

It mentions: "but I need the 0 in the front". It does not mention number of zero and the length of the number (number of digits). – doptimusprime Dec 28 '13 at 16:42
It'd worked but I need the zero to convert the binary number. Thanks anyway! – user3075022 Dec 28 '13 at 16:45

score 0 · Answer 4 · answered Dec 28 '13 at 16:51

0

Why so complicated and not just do directly:

printf("%d%d%d%d", comp[cont][0], comp[cont][1], comp[cont][2], comp[cont][3]);

answered Dec 28 '13 at 16:51

alk

Because it's a binary number and I need to concatenate it and convert to decimal – user3075022 Dec 28 '13 at 16:54

4 Answers4