My loop is executing more times then expected

Asked Jan 24 '18 at 18:29

Active Jan 24 '18 at 18:52

Viewed 52 times

Hi I wrote a function that inputs a string from a file and then prints out the answer, now my loop is executing more then the file has lines: this is my code :

    void CalculateAll()
{
    char str[SIZE];
    int ans;

    FILE* p = fopen("Expressions.txt", "r");
    if (p == NULL)
    {
        printf("FAIL");
        return;
    }
    while (!feof(p))
    {
        int i = 0;
        fgets(str, SIZE - 1, p);
        while (str[i] != '\n')i++;
        str[i] = 0;

        ans = CalculateExpression(str);
        printf("%d\n", ans);
    }


}

the file has

121 + 34 =
562 + 45 =
100 / 10 =

the output should be

155 
607 
10

but instead I get :

and my loop is running again even tho I reached the end of the file, does anyone have an idea? EDIT: its not the same question..

When I changed my code to this my first line is gone :

void CalculateAll()
{
    char str[SIZE];
    int ans;

    FILE* p = fopen("Expressions.txt", "r");
    if (p == NULL)
    {
        printf("FAIL");
        return;
    }
    while ((fgets(str, SIZE - 1, p)))
    {

        int i = 0;
        fgets(str, SIZE - 1, p);
        while (str[i] != '\n')i++;
        str[i] = 0;

        ans = CalculateExpression(str);
        printf("%d\n", ans);
    }


}

edited Jan 24 '18 at 18:52

asked Jan 24 '18 at 18:29

possibly relevant: https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong – Christian Gibbons Jan 24 '18 at 18:30
1

where do you check the null character '\0' ? If your last line doesn't contain a '\n' the while loop goes over.. – Roberto Trani Jan 24 '18 at 18:32
ok so its wrong to use, but how do I use that with fgets? – Jan 24 '18 at 18:32
@Roberto Trani I read from a file, I made a function that knows how to decipher the string, the problem is its doing 1 more loop then needed. – Jan 24 '18 at 18:34
Why does code not check the return value of `fgets()`? – chux - Reinstate Monica Jan 24 '18 at 18:35
@chux how exactly? while(fgets()!=EOF)? – Jan 24 '18 at 18:36
Who or what text suggested `while (fgets()!=EOF)`? – chux - Reinstate Monica Jan 24 '18 at 18:38
then how do you check the value of fgets ? because its a pointer , and impossible to check like the duplicated question you suggested. – Jan 24 '18 at 18:39
Something like `if (!fgets()) break;` – Ove Jan 24 '18 at 18:40
But actually `while (fgets()) { ... }` would indeed probably be better, see the currently 4th answer in the duplicate question. – Ove Jan 24 '18 at 18:43
@Ove actualy no, now my first line is gone – Jan 24 '18 at 18:44
if I do while(fgets()) my first line is gone, instead of the extra one. – Jan 24 '18 at 18:48
Maybe your rewrite isn't right and you're making two loops instead of the one you should? Show your revised code if you're still having issues. – Ove Jan 24 '18 at 18:50
@Ove I edited the post and added the rewritten code. – Jan 24 '18 at 18:53
1

ohh I see the issue. I did 2 fgets.. thats why... stupid me – Jan 24 '18 at 18:54

My loop is executing more times then expected

0 Answers0