CODEWITHSUNDEEP
carrays
Tursko
Tursko

Reputation: 132

Scanning text file into an array?

I have a text file, lets call it numbers.txt, and I need to scan it into an array.

numbers.txt (below is what is inside)

8 2 5 9 10 4 11 -1

The special value -1 indicates the end of the list.

I'm kinda confused on how to get it into my array. I know I need a loop, but can't put my head around it. Also, I am not scanning the file within the program, I am doing it within the terminal.

taylor> file < numbers.txt

So I would set it up like the user is inputting it.

 int main()
 {
    int numbers[50];
    int n, i;
    //scanf("%i", &n) 
    for(i = 0; i < 50; i++)
    {
        //not sure what to do
    }
 }

Upvotes: 1

Views: 520

Answers (2)

user3629249
user3629249

Reputation: 16540

the posted code does not compile! it is missing the #include statements

Here is a version of the code that:

  1. cleanly compiles
  2. follows the axiom: only one statement per line and (at most) one variable declaration per statement.
  3. checks for I/O errors and announces them on stderr
  4. contains the needed #include statements
  5. for readability and ease of understanding: separates code blocks (for, if, else, while, do...while, switch, case, default) via a single blank line
  6. removes unused variables
  7. if/when reads the -1 exits the read loop
  8. avoids using 'magic' numbers, by giving them meaningful names

and now the code

 #include <stdio.h>  // scanf(), perror()
 #include <stdlib.h> // exit(), EXIT_FAILURE

 #define MAX_NUMBERS 50

 int main( void )
 {
    int numbers[ MAX_NUMBERS];
    int i;

    //scanf("%i", &n)
    for(i = 0; i < MAX_NUMBERS; i++)
    {
        if( 1 != scanf( "%d", &numbers[i] ) )
        {
            perror( "scanf for number failed" );
            exit( EXIT_FAILURE );
        }

        // implied else, scanf successful

        if( -1 == numbers[i] ) break;
    }
 }

Upvotes: 0

chux
chux

Reputation: 153457

OP needs to account for many stopping conditions.

  1. Data read is -1 per OP's deleted comment "... I want it to stop once it its -1. So like while(!=-1) run the loop. I could do that with if statements as well." . This is detectable by testing the value read.

  2. Only up to 50 numbers. Test the count of numbers read.

  3. Not more input (end-of-file). This is detectable by testing the scanf() return value of EOF.

  4. Rare input error. (example, keyboard cable broke.) This is also detectable by testing the scanf() return value of EOF.

  5. If the input was non-numeric. This is detectable by testing the scanf() return value of 0.

  6. If the input text was in range of int. Detection for this is not shown below.

  7. Unclear if all data needs to be on one line, so detecting a '\n' is needed. Detection for this is not shown below.

Example

 int main()
 {
    int numbers[50];
    int i = 0;
    for( ; i < 50; i++) {
      int n;
      int conversion_count = scanf("%i", &n);
      if (conversion_count != 1) {
        break;  // End-of-file, input error, non-numeric input
      }
      if (n == -1) {
        break;
      }
      numbers[i] = n;
    }
    printf("%d numbers read.\n", i);
 }

Upvotes: 2

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