Weird end values when reading from file using fgetc()

Question

I'm using fgetc() to read a char from a file which consists of digits only. Then I convert the characters to int and print it out. That's fine. But after printing out all the digits, at the end I get -38-49 values. I googled it, but nothing about it there. In the input file, I have the following: 0105243100000002200000010001318123 The outpuf is like this: 0105243100000002200000010001318123-38-49 My code:

do
    {
        c1 = fgetc(fread)-'0';
        if (!isspace(c1))
        {
            printf("%d", c1); 
        }       
        if (feof(fread))
        {
            break;
        }
    } while (1);

Answer 1

You are reading the newline (10) and the EOF return value of fgetc (-1). Substracting '0' (48) from those yields those negative numbers.

Check if the char if valid, it must be in range ['0','9']

c1 = fgetc(fread);
if(c1 >= '0' && c1 <= '9') {
  c1 -= '0';
  // ...
}

Answer 2

When reading a file with fgetc you should check for EOF first, to detect the end of the file

int c, n;
while ((c = fgetc(f)) != EOF) {
    if (isdigit(c)) {
        n = c - '0';
        printf("%d", n);
    }
}

Otherwise, you use the EOF value and get the negative result.