getting 1000 chars at a time from stdin

Hi all,

My program has needs to ask for standard input.. the user can enter a single number (that could be millions of digits long) and i need to get 1000 digits at a time.

Which function should i use? fgets()? but im not sure where i specify the 1000 digit buffer? Here is what i tried, could some one tell me what im doing wrong.

Thank you :)

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main (int argc , char** argv) {

        int buffer[1000];
        int current;
       
        while (current = fgetc(stdin) != '\n') {
               
                current = current - '0';
               
                printf("&#37;d", current);
        }
       
        return 0;
}

---

Without using a specialized library, the maximum size for a number is 1E+37 when you store it as a float, this value is defined in float.h under the macro FLT_MAX. If you store it as an unsigned long, the biggest value is ULONG_MAX or 4294967295.

If you want to store bigger numbers, find yourself a specialized library or read and store the number inside an array, where each place in the array could be of a numeric type, for example integer. But then you had to define your own operations so you could actually use that number.

What do you need this for anyway ?

And to answer your question:

Code:

---

int maxSize = 1000;
char myArray[maxSize];
while ((fgets(myArray, maxSize, stdin) != NULL)
{
  // stuff
}

---

Quote:

---

Originally Posted by KONI

Without using a specialized library, the maximum size for a number is 1E+37 when you store it as a float, this value is defined in float.h under the macro FLT_MAX. If you store it as an unsigned long, the biggest value is ULONG_MAX or 4294967295.

If you want to store bigger numbers, find yourself a specialized library or read and store the number inside an array, where each place in the array could be of a numeric type, for example integer. But then you had to define your own operations so you could actually use that number.

What do you need this for anyway ?

And to answer your question:

Code:

---

int maxSize = 1001;
char myArray[maxSize]; /* C99 only */
while ((fgets(myArray, maxSize, stdin) != NULL)
{
  // stuff
}

---

---

Since we assume you wanted a 1000 digit number, you'll have to leave room for the null (and/or newline).


Quzah.

thanks :).. but it keeps asking the user to input a number. I only require the user to enter 1 number.. how do i prevent it from continually asking.

thanks.

i think you guys dont understand.. i need to receive a really large number from stdin, then get 1000 digits at a time from that big number. The code given is fine.. just it keeps asking for more input.. i just want to ask for input once.. and parse 1000 digits at a time, digit by digit.. if you get what i mean?

please help, thanks :)

Very impatient. You didn't even wait an entire hour. LOL.

This is something you should be able to do. Your programming is looping and you want to stop it. So take the loop out. :rolleyes:

but i need the loop right? cause what will happen if the input number is greater than 1000 digits long... i need to read the next lot of digits in right?

Depends which block of code you're using. Thought you were using the one given to you that uses fgets() since you thanked him for the code and commented on it. If that is the case, the number is already read in one statement, unless you think the number could be greater than 1000. What you need to do then is check if the last char of the buffer (ie. buf[strlen(buf)-1]) is equal to '\n'. If it is, then you've read the number, and you can leave the loop.

k, this seems to work, but not sure if its logically right. Does this seem ok to you?

Code:

---

#include <stdio.h>
#include <stdlib.h>

int main (int argc , char** argv) {

        int counter = 0;
        int maxSize = 1001;
        char myArray[maxSize];

       

        while (myArray[counter] != '\n' && fgets(myArray, maxSize, stdin) != NULL ) {
               
                for (counter=0; counter<maxSize; counter++) {
                       
                        if (myArray[counter] != '\n') {
                                printf("&#37;d", myArray[counter]-'0');
                        }
                        else {
                                break;
                        }
                }
               
        }
       
        return 0;
}

---

Did you even test it? I think not.

yes, why is something wrong?

Quote:

---

Originally Posted by waxydock

Code:

---

        while (myArray[counter] != '\n' && fgets(myArray, maxSize, stdin) != NULL ) {

---

---

On the first iteration through this loop, counter is zero, but myArray[counter] is some uninitialized value. So just BY CHANCE, this value could happen to be '\n' in which case your loop terminates before it reads a single byte.

Before you start the loop, set myArray[0] = '\0';

Also, although you do loop over and over, you simply overwrite the data you previously read. Thirdly, declaring myArray[maxSize] is not standard C (unless you are talking about C99). And since maxSize could conceivably be huge, even if it was standard, it would still be a bad idea.

Also, you have very little error checking: what happens if one of the characters entered was not a space, newline, or digit?

There doesn't have to be a newline at the end of stdin. DOS at least allows you to put an EOF at the end of a non-blank line:

Code:

---

some text^Z

---

So checking for one as your ending condition is probably a bad idea. I would just skip spaces and newlines if you encounter them, and terminate on a '\0'. Of course, you'd then have to set myArray[0] to something other than '\0', or, better yet, use a do-while loop instead of a while loop.

Also, you do not use anything from <stdlib.h>, so you don't have to include it.

Turn on compiler warnings! Nearly every compiler could have told you that you were using myArray without initializing it. For Dev-C++, add -W -Wall -ansi -pedantic to the compiler's command line in the Compiler Options dialog.

Hi,

I had a go at what you guys said but im having a problem when i enter a really big number in. The final digit in the large number is not printed... any ideas?

Code:

---

#include <stdio.h>

#define maxSize 10001

int main (int argc , char** argv) {

        int counter = 0;
        char myArray[maxSize];
       
        myArray[0] = '\1';
       
        while (myArray[counter] != '\n' && myArray[counter] != '\0' && fgets(myArray, maxSize, stdin) != NULL ) {
               
                for (counter=0; counter<maxSize; counter++) {
                       
                        if (myArray[counter] != '\n' && myArray[counter] != '\0') {
                                printf("&#37;d", myArray[counter]-'0');
                        }
                        else {
                                break;
                        }
                }
               
        }
       
        return 0;
}

---

1 - You're trying to check the contents of the array before you ever actually fill it up.
2 - You're checking the contents of the array in the outer loop, instead of just breaking from it.
3 - \1 isn't a valid escape sequence.
4 - You assume all input is actually a digit, instead of just checking to be sure.


That'll get you started.


Quzah.