C Program - Validate numbers read from a text file

Question

I am reading 15 numbers from a text file, with each number in a new line:

As you can see from the code I need the numbers to be validated so they are less than 26, otherwise terminate the program.

At the moment I am validating only after inserting it to the array (numArray). Is there a cleaner way of doing it (to validate before inserting to the array)?

The problem is, I can't seem to get the actual line in the text file that's being read. That's why I've validated it using the loop index on the array (int x = numArray[i];).

Any help is appreciated, I'm quite new to C programming. Thanks.

FILE *myFile = fopen(dataset.txt, "r");
int numArray[15];

if (myFile != NULL) {

    for (int i = 0; i < sizeof(numArray); i++)
    {
        //insert int to array
        fscanf(myFile, "%d", &numArray[i]);

        //Validate number
        int x = numArray[i]; 
        if (x > 25) {
            printf("Invalid number found, closing application...");
            exit(0);
        }
    }

    //close file
    fclose(myFile); 
}
else {
    //Error opening file
    printf("File cannot be opened!");
}

1. Check return value of `fscanf` in case file has other characters than just numbers. 2. Why are you putting the numbers in the array anyway, is that a necessary step for later code? Anyway you aren't really *inserting* anything, you are just setting values at array indexes (inserting would generally imply shifting elements in order to make room in the middle). — hyde, Oct 07 '16 at 20:02
Your loop will go out of bounds of the array. The `sizeof` operator gives you the size in ***bytes***, not the number of elements. For an actual array (like your `numArray`) you can get the number of elements by dividing the size of the full array with the size of a single element, i.e. `sizeof numArray / sizeof numArray[0]`. — Some programmer dude, Oct 07 '16 at 20:02

score 1 · Accepted Answer · answered Oct 07 '16 at 20:04

of course you can store it in a local variable and assign only if valid. But since you're calling exit(0) if invalid it doesn't change anything. I suppose you want to break from the loop instead.

BTW your loop is wrong. you have to divide sizeof(numArray) by the size of one element otherwise you'll loop too many times and you'll crash the machine if there are too many numbers in your input file (yes, I also added a test for end-of-file)

if (myFile != NULL) {

    for (int i = 0; i < sizeof(numArray)/sizeof(numArray[0]); i++)
    {
        int x; 
        //insert int to array
        if (fscanf(myFile, "%d", &x)==0)
        {
            printf("Invalid number found / end of file, closing application...\n");
            exit(0);  // end of file / not a number: stop
        }

        //Validate number
        if (x > 25) {
            printf("Invalid number found, closing application...\n");
            exit(0);
        }
        numArray[i] = x;
    }

    //close file
    fclose(myFile); 
}

C Program - Validate numbers read from a text file

1 Answers1