合并排序 Arrays

Question

I am beginner in C programming. I have been doing these for hours, but I couldn't produce the needed output.

Input: 1 2 3 4 5 : 6 7 8 9
Output: 1 2 3 4 5 6 7 8 9

Input: 1 3 4 5 6 7 8: 1 2 10
Output: 1 1 2 3 4 5 6 7 8 10

Input: 2 3 9: 1 2 4 5
Output: 1 2 2 3 4 5 9

Basically, the input consist of two arrays separated by a colon. I know how to merge and sort them but my problem is that colon. So far, here is the code I've created:

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

int main()
{
    int a[100],b[100];
    int i;
    
     printf("Enter elements in array:");

     do 
     {
    scanf("%d", &a[i++]);
     } while(getchar() != ':');

    int size1=i;

    for(i=0; i<size1; i++)
    {
        printf("%d",a[i]);
    }
    
  return 0 ;
}

This works in reading the second and third test case, however, the first one seems to produce numbers it shouldn't.

Second Test Case

What should I do? Any help would be appreciated, please. Thank you so much.

Answer 1

Using scanf() isn't necessarily the right tool here. The reason is that it does not recognize that your user pressed the Enter key to indicate the end of input.

Better to read a line of text, then parse it to an array of whatever type you want. You can even use sscanf() in a loop to do it!

#include <stdio.h>
#include <string.h>

int main(void)
{
    // Each array should also have a SIZE (number of elements being used)
    int A[100],     B[100];
    int A_size = 0, B_size = 0;  // Initially, no elements are being used

    // Ask the user for input and get it as a STRING
    printf("Enter arrays (separated by colon): ");
    char s[1000];
    fgets(s, sizeof s, stdin);
    
    // Now we are going to use sscanf() to traipse the string.
    char * p = s;  // `p` is our current position in the string
    int    n = 0;  // `n` is the number of characters last scanned by sscanf()

    sscanf(p, " %n", &n);  // skip any leading whitespace

    // For each successful scan of WHITESPACE INTEGER WHITESPACE:
    //   update the size of A[]
    while (sscanf(p+=n, "%d %n", A+A_size, &n) == 1) A_size += 1;
    if (*p != ':') return 1;  // sscanf() should have failed to read an integer at ':'

    // Prepare for the next loop by scanning past the colon (and eating any whitespace)
    sscanf(p, ": %n", &n);
    
    // For each successful scan of WHITESPACE INTEGER WHITESPACE:
    //   update the size of B[]
    while (sscanf(p+=n, "%d %n", B+B_size, &n) == 1) B_size += 1;
    if (*p) return 1;  // sscanf() should have reached the end of the string
    
    // Let’s print what we got from the user
    printf("A[%d] =", A_size);  for(int i=0; i<A_size; i++) printf(" %d", A[i]);  printf("\n");
    printf("B[%d] =", B_size);  for(int i=0; i<B_size; i++) printf(" %d", B[i]);  printf("\n");

    return 0 ;
}

To be fair, doing stuff like this is tricky as hell. I even wrote an old answer all about using file I/O style functions on a string that explains the mechanism I used here.

Better, maybe, is to simply tokenize the string and convert its parts.

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

int main(void)
{
    int A[100],     B[100];
    int A_size = 0, B_size = 0;

    printf("Enter arrays (separated by colon): ");
    char s[1000];
    fgets(s, sizeof s, stdin);
    
    // Now we are going to tokenize the string. 
    // To do that we first need to split it between A and B:
    char * colon = strchr(s, ':');
    if (!colon) return 1;
    *colon = '\0';
    
    // Now we will use strtok() to get the individual elements of A[]
    for (char *token, *start = s;  (token = strtok(start, " \n\r\t"));  start = NULL)
    {
      // Use any method you like to perform the conversion to int.
      // For this example, I will just use this fictitious helper function:
      A[A_size++] = convert_to_integer(token);
    }
    
    // Rinse and repeat for B[].
    for (char *token, *start = colon+1;  (token = strtok(start, " \n\r\t"));  start = NULL)
    {
      B[B_size++] = convert_to_integer(token);
    }
    
    // Let’s print what we got from the user
    printf("A[%d] =", A_size);  for(int i=0; i<A_size; i++) printf(" %d", A[i]);  printf("\n");
    printf("B[%d] =", B_size);  for(int i=0; i<B_size; i++) printf(" %d", B[i]);  printf("\n");

    return 0 ;
}

While less so, using strtok() is still tricky, so take care. I had originally written the loop by punning the token value with start . But then I figured that was likely too confusing. Nevertheless it is a common C idiom you will see.

for (char *token = s;  (token = strtok(token, "..."));  token = NULL)
{
  do_something_with(token);
}

The hypothetical convert_to_integer() function is tricky too. Not because it is a helper, but because converting a string to integer in C is tricky — all kinds of things can go wrong if input doesn't conform. But that is a separate discussion.

To recap:

1. Get user input as a string (a single line of input)
2. Attempt to convert user input to your desired data

Processing user input as an array has added complexity, but it is not unmanageable.

EDIT: Oh, I should notice to you that I considered empty arrays as valid input. (You should definitely test your Merge function against one or more argument arrays being empty.)

1 2 3:
:7 9
: