2

I'm trying to declare an array of size 10,000. Preferably a character array. Then I may take the input of any size n(<=10,100). And I want to find this n.

I have a code which is not working.

int main()
{
    char arr[10000];
    cin >> arr;
    cin.sync();
    int l=0;
    for(int i=0; ; i++)
    {
        if(arr[i]=='\n')
            break;
        l++;
    }
    cout << l;
    return 0;

Input : Hell I expect the output to be 4, but the actual output is 4482.

Blaze
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Umar Malik
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    You use `std::vector`. [VLA:s](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard) are not allowed in standard C++ – Ted Lyngmo Jun 03 '19 at 09:02
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    Since `std::cin` stops reading on encountering the first ***whitespace*** `arr` will ***never*** contain a `'\n'`. – David C. Rankin Jun 03 '19 at 09:27
  • @TedLyngmo `char arr[10000];` isn't a VLA (it's just a plain old array declared with an integer constant) – David C. Rankin Jun 03 '19 at 09:29
  • Consider using a `std::string` and [`std::getline`](https://en.cppreference.com/w/cpp/string/basic_string/getline). – Bob__ Jun 03 '19 at 09:32
  • @DavidC.Rankin No, but OP's question is about how to create a VLA. The code doesn't reflect it though. – Ted Lyngmo Jun 03 '19 at 10:24

3 Answers3

3

You can't do that in standard C++. But you can use 

std::vector<char> arr;

and arr.resize(/*ToDo - size here*/) when you need to. The std::vector memory management is also superior to using a large fixed-size array with automatic storage duration.

That said, a std::string is probably the best choice in your case:

std::string the_standard_library_is_fantastic;
std::cin >> the_standard_library_is_fantastic;

followed by

std::cout << the_standard_library_is_fantastic;

Your assumption that arr is in a sense terminated with a '\n' is not correct.

Bathsheba
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1

cin >> arr; puts a C-style string into arr, which is terminated with '\0', not with '\n' (even though you press enter to send the input to your program). To get that expected output of 4, you need to change this 

if (arr[i] == '\n')

To this:

if (arr[i] == '\0')
Blaze
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0

Use standard C++ library normally. #include <string> does this task easily.

string arr;
cin >> arr;
cin.sync();
int l = arr.length();
cout << l;
return 0;
Faruk Hossain
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