What happens if I enter a character to a dynamically/statically allocated double array?

Question

Right now I am using a dynamically allocated double array. How can I check if someone has entered a character?

double* scanarray(int length)
{
    double* arr;
    arr = (double*)malloc(sizeof(double)*length);
    printf("Enter %d real numbers: \n", length);
    for (int loop = 0; loop < length; loop++)
        scanf_s("%lf", &arr[loop]);
    return arr;
}

You don't enter a character. You use `scanf_s` to scan doubles... — StoryTeller - Unslander Monica, Mar 01 '17 at 08:59
Also you should decide if you are using C or C++ - in C you shouldn't cast the return of `malloc` while in C++ you shouldn't use `malloc` at all — UnholySheep, Mar 01 '17 at 09:01
In C a pointer to void can be assigned (promoted) to pointer of any type without a cast. — Ajay Brahmakshatriya, Mar 01 '17 at 09:06
The line `arr = (double*)malloc(sizeof(double)*length);` should be `arr = malloc(sizeof(double)*length);`. See [this answer](http://stackoverflow.com/a/605858/2878796) for a detailed explanation — UnholySheep, Mar 01 '17 at 09:09
@anti mage: What exactly do you mean by "entered a character"? If someone enters `123a`, does that qualify as "entered a character" or not? — AnT stands with Russia, Mar 01 '17 at 09:19
@anti mage: You shouldn't cast the result of `malloc` because there's absolutely no reason for doing so. When you need to calculate `3 + 2` you just say `3 + 2`, not `(int) ((int) 3 + (int) 2)`, don't you? If so, then why are you doing this `(double*)` thing with `malloc`? In fact, it should be `arr = malloc(length * sizeof *arr)`. No mention of `double` at all. — AnT stands with Russia, Mar 01 '17 at 09:21
@AnT Yes, it does qualify for "entered a character". The array should only have real numbers. — anti mage, Mar 01 '17 at 09:24
@anti mage: `scanf` does not provide you with any credible means to reject such inputs as `123a`. From `scanf`'s point of view, this is a prefectly valid input. If you want to reject it, forget about `scanf`ing numbers directly. Read strings and then parse, validate and convert them to numbers manually (i.e. by separate library functions like `strtod`) — AnT stands with Russia, Mar 01 '17 at 09:26

score 2 · Answer 1 · answered Mar 01 '17 at 09:14

You could check return value of scanf (and related functions such as scanf_s):

Return Value

Each of these functions returns the number of fields that are successfully converted and assigned; the return value does not include fields that were read but not assigned. A return value of 0 indicates that no fields were assigned. The return value is EOF for an error or if the end of the string is reached before the first conversion.

https://msdn.microsoft.com/en-us/library/t6z7bya3.aspx

What happens if I enter a character to a dynamically/statically allocated double array?

1 Answers1

Return Value