Integer array with whitespace characters output

The idea is get the line as input and then parse it to get the integers using strtol etc. The line you will get using fgets. And then you will store it in array. There are two options now,

• If you get more elements than you can hold in the array then you will show error when the array is full.

• Or use dynamically allocated memory which will grow as the number you enter increase.

I am afraid, using scanf until you get integers is an option - but that is not the good idea and scanf is not the easy way to go about this.

the following proposed code:

1. cleanly compiles
2. follows the axiom: only one statement per line and (at most) one variable declaration per statement.
3. is consistently indented
4. eliminates unneeded variables
5. limits the scope of variables
6. performs the desired functionality
7. properly checks for error indications from system functions
8. documents why each header file was included
9. all 'magic' numbers given meaningful names (via #define statement)

and now the proposed code:

#include <stdio.h>     // scanf(), fprintf(), stderr, printf()
#include <stdlib.h>    // exit(), EXIT_FAILURE


#define MAX_NUMS_PER_PERSON 3


int main( void )
{
    int alice[ MAX_NUMS_PER_PERSON ]={0};
    int bob[ MAX_NUMS_PER_PERSON ]={0};

    //enter alice
    for( int i=0; i< MAX_NUMS_PER_PERSON; i++ )
    {
        if( 1 != scanf("%d", &alice[i]) )
        {
            fprintf( stderr, "failed to input nums for Alice\n" );
            exit( EXIT_FAILURE );
        }

        // implied else, scanf successful
    }

    //enter bob
    for( int i=0; i< MAX_NUMS_PER_PERSON; i++ )
    {
        if( 1 != scanf("%d", &bob[i]) )
        {
            fprintf( stderr, "failed to input nums for Bob\n" );
            exit( EXIT_FAILURE );
        }

        // implied else, scanf successful
    }


    //print alice
    for( int i = 0; i < MAX_NUMS_PER_PERSON; i++)
    {
        printf("%d ", alice[i]);
    }

    //print bob
    for( int i = 0; i < MAX_NUMS_PER_PERSON; i++)
    {
        printf("%d ", bob[i]);
    }

    return 0;
}

Changed my C program according to this answer

Putting numbers separated by a space into an array

#include <stdio.h>
#include <ctype.h>

#define ARRAY_SIZE 3

#define BOB_SIZE    5
#define ALICE_SIZE  4

int main()
{
    int tmp, i=0;
    char follow;
    int count;
    int a[ALICE_SIZE]={0}, b[BOB_SIZE]={0};

    if((ALICE_SIZE < ARRAY_SIZE) || (BOB_SIZE < ARRAY_SIZE))
    {   
        printf("Not sufficient space in array, check the sizes.\n");
        return -1;
    } 

    while ((i < ARRAY_SIZE) && (count = scanf("%d%c", &tmp, &follow)) > 0)
    {
      if ((count == 2 && isspace(follow)) || (count == 1))
      {
        a[i++] = tmp;
      }
      else
      {
        printf ("Bad character detected: %c\n", follow);
        break;
      }
    }

    i=0;

    while ((i < ARRAY_SIZE) && (count = scanf("%d%c", &tmp, &follow)) > 0)
    {
      if ((count == 2 && isspace(follow)) || (count == 1))
      {
        b[i++] = tmp;
      }
      else
      {
        printf ("Bad character detected: %c\n", follow);
        break;
      }
    }

    for(i = 0; i < ARRAY_SIZE ; i++)
        printf("%d ", a[i]);

    printf("\n");
    for(i = 0; i < ARRAY_SIZE ; i++)
        printf("%d ", b[i]);

    return 0;
}

Tried to make input as general as possible while using scanf looks like too much effort but its required to make it robust,and put corner cases and errors.

More problems with scanf comes with strings or %s specifier. So better get used to fgets, strtol and dynamic arrays in parsing while giving inputs.