Scan multiple integers without knowing the actual number of integers

Question

I have to input values whose frequency i don't know...

For example first input: 1 32 54 65 6

second input: 2 4 5

What i first thought was, scan the values, if new line '\n' then break the loop, but that didn't go so well, so instead i said i use characters, then i typecast to get the number but the problem with this also came that it scan one character by one and if its its a negative value its also a problem;

Something like this

#include <stdio.h>

int main(){
int myarray[20];
int i=0, data;

while(1){
      scanf("%d", &data);
      if (data == '\n') break; 
      myarray[i]=data;
}

return 0;
}

but then, scanf jumps all the special characters and look for only ints... is there a way to scan ints to an array and when there is a newline it stops?

You can read a whole line, split it on e.g. whitespace, and then convert each part to integers. — Some programmer dude, Nov 26 '14 at 11:03
Use `fgets()` to read the line and followed by it use `sscanf()` — Gopi, Nov 26 '14 at 11:04
For readability I strongly recommend to put `break;` into a new line. Though this may be a matter of taste. — TobiMcNamobi, Nov 26 '14 at 11:05

Sourav Ghosh · Accepted Answer · 2015-06-12T07:05:15.243

6

My advice, go for fgets().

Read the whole line from the input
Tokenize using space [] [or your preferred delimiter] [using strtok()]
Allocate memory to store the integer
Convert the string input to integer [maybe strtol()] and store each integer.

Optionally, you may want to add some validation and error checking.

Read more about fgets() here.

^{also, don't forget to get rid of the trailing \n stored in the read buffer by fgets()}

edited Jun 12 '15 at 07:05

answered Nov 26 '14 at 11:04

Sourav Ghosh

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I see fgets get a string, if i change the data into string using say strtol or atoi am not quite sure if its going to recognize negative values?? – user3564573 Nov 26 '14 at 11:13
@user3564573 if you notice, the return type is `long int` for `strtol()` and I see no reason not to hadle negative numbers. as for delimiter, you cannot use `-` sign as a delimiter. – Sourav Ghosh Nov 26 '14 at 11:15
@user3564573 Read the manual page for `strtol()` if you're not familiar with it. Hint: it handles negative values just fine. – unwind Nov 26 '14 at 11:16
Thanks, let me try it out – user3564573 Nov 26 '14 at 11:17
Note that `strtok_r` is not a standard function in C, but a common extension in many compilers. – chux - Reinstate Monica Nov 26 '14 at 15:38
A limitation with this approach is that the maximum line length needs to be known ahead of time (unless code uses `fgets()` multiple times on the same line - somewhat complicated) and OP implies an unknown count of numbers per line. IMO such a limitation is not bad, but code should report when a line is read that is longer than expected. – chux - Reinstate Monica Nov 26 '14 at 15:46
@chux Thank you sir for mentioning the `extension` regarding `strtok_r()`. Also, by mentioning `some validation and error checking`, I implied the read buffer length overrun, nevertheless, thanks for elaboration. – Sourav Ghosh Nov 26 '14 at 16:04
The link to the documentation should be as follows -> https://linux.die.net/man/3/fgets – Jean-Victor Côté May 22 '17 at 20:14
@Jean-VictorCôté emmm...did you miss `Read more about fgets() here.` part? – Sourav Ghosh May 23 '17 at 02:17

score 0 · Answer 2 · edited May 23 '17 at 10:30

Recommend using fgets() as suggested by Sourav Ghosh

Otherwise code can search for '\n' before reading each int

#include <ctype.h>
#include <stdio.h>
#define N (20)

int main(void) {

  int myarray[N];
  int i = 0;

  while (1) {
    int ch;
    while (isspace(ch = fgetc(stdin)) && ch != '\n')
      ;
    if (ch == '\n' || ch == EOF)
      break;
    ungetc(ch, stdin);

    int data;
    if (scanf("%d", &data) != 1)
      break; // Bad data
    if (i < N)
      myarray[i++] = data;
  }

  return 0;
}

Scan multiple integers without knowing the actual number of integers

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