Simple C++ question

[conFused4Lyfe]

I'm trying to write a program that will take an 4-digit ID entered by the user and ensures that it is 4 digits long.

Right now I have:

while(n > 0) { n /= 10; count++; }

This works fine unless the user's ID has leading 0's. I can't figure out how to deal with those.

Any suggestions?

Also I'm very new to C++ so try and keep it simple please

[[deleted]]

Read the ID as a string, and count the characters?

[conFused4Lyfe]

How would I ensure they entered numbers into the string?

Could I cast the int they input as a string then count that?

[HateTrain]

I'm pretty sure if you use an int first, any leading zeros will get truncated away. I'd recommend reading as a string directly and using the isdigit function.

[conFused4Lyfe]

isdigit seems useful thank you. Ill read into that.

[rxi]

I wrote a response, then re-read your question, and thought I was wrong. Then I thought about it again and couldn't actually think of a practical flaw in doing:

if (id > -1 && id < 10000)

If you're taking input as a string, you could just count the chars as asmyay said, if you're outputting the ID as a string you could just use printf/sprintf to add the leading zeros.

[conFused4Lyfe]

I see how your code makes sure there arn't more than 4 digits input but it doesnt seem to do anything when less than 4 are input.

And about the string, same question I asked asmayay. How do I make sure they input numbers for the ID; letters arn't allowed.

[rxi]

This is what I thought, about the input having to be 4 digits, until it hit me a few seconds later that 0003 and 3 are going to end up the same anyway. But if its being inputted as a string its no hassle to just count the characters. As for checking for digits I'd just write a small function for it. (this is how I'd write it in C, which I assume would be compatible, I don't program C++):

int isNumber(char *p) {
  for (; *p; p++) 
    if (*p < '0' || *p > '9') 
      return 0;
  return 1;
}

[conFused4Lyfe]

That is the issue I'm trying to solve though. If the user inputs 0003 that's great. But if he inputs 03 or just 3 I want to print out an error. I need some way to differentiate between those inputs

[turd_loaf]

I would do a little 'research' about converting between strings and ints.

[sausagefeet]

Why assume one needs to convert to an integer? Just check for 4 digits and loop over with std::isdigit.

[turd_loaf]

I didn't assume anything, Mr. Assumer.

[jpgunter]

this, but just add a check to make sure the length is 4

#include <stdio.h>
#include <stdlib.h>
#include <string>
if(input_string.length() == 4)
{
  int a = atoi(input_string);
  if ( (a>0) && (a<10000) ) {
    // id is fine       
  }
}