Denote number of elements in an array with input?

Question

Here is the input:

First line of input file contains a single integer T which denotes the number of test cases. For each test case, there will be two lines. First line contains N which denotes number of elements in an array, and second line contains N space seperated integers.

I know how to denote the number of test cases but not how to denote numbers of elements in an array. I'm pretty new to c++ , so it would be nice if you answer noob friendly.

You can use a `std::vector values` then `values.resize(T)` where `T` is the `int` you read from the previous line. And if `vector` is new to you, that is like an array with a size that is only known at run time, instead of compile time. — Cory Kramer, Jun 09 '20 at 17:33
This should be of use: https://stackoverflow.com/q/388242/2079303 — eerorika, Jun 09 '20 at 17:33
Hello @Kedog , see my updated answer and tell me whether you want to understand anything more? — KL_KISNE_DEKHA_HAI, Jun 09 '20 at 18:53
Hey @Kedog if you are done with the question please mark the answer as well. — KL_KISNE_DEKHA_HAI, Jun 11 '20 at 03:46

KL_KISNE_DEKHA_HAI · Answer 1 · 2020-06-09T18:47:02.657

1

It should be something like this :

cin>>test;                                // Taking the number of test cases 
    while(test--){                        // For each test case
        cin>>n;                           // Taking input n
        vector<int> a(n);
        for(i=0;i<n;i++){
            cin>>a[i];                   // Taking input as n integers
        }
    }

OR

cin>>test;                                     // Taking the number of test cases  
    for(int i=0;i<test;i++){                   // For each test case
        cin>>n;                                // Taking input n
        vector<int> v;                         // declaring a vector
        for(int j=0;j<n;j++){
            cin>>x;
            v.push_back(x);                    // Taking input as n integers one by one
        }
    }

edited Jun 09 '20 at 18:47

answered Jun 09 '20 at 17:54

KL_KISNE_DEKHA_HAI

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I did not get what you are trying to state.. The question asked is common way to input in many competitive coding sites, so i answered accordingly, also c++11 , c++14 ,c++17 all these compilers accept this format. I myself have done it. Also i have stated a vector method using push_back as another way. – KL_KISNE_DEKHA_HAI Jun 09 '20 at 18:29
ok , so basically in this https://www.onlinegdb.com/online_c++_compiler ,are we using an extension? Also many of the red coders in codeforces too used the way i stated , so i did not doubt it. Anyways i have updated the answer. Please have a look. – KL_KISNE_DEKHA_HAI Jun 09 '20 at 18:39
Yes it's using an extension - and I couldn't find a way to turn the extension off. With the online compiler I linked to you can, so if you'd like to get more help from the compiler to stay within the standard I suggest that you try that one out. – Ted Lyngmo Jun 09 '20 at 18:44
1

Is it fine now? please see. – KL_KISNE_DEKHA_HAI Jun 09 '20 at 18:47
Yes. You got my vote and I removed my old comments regarding the VLA. – Ted Lyngmo Jun 09 '20 at 18:50
1

Thank you @Ted Lyngmo , i will let my comments remain as it may help others who may be in the same misconception . :) – KL_KISNE_DEKHA_HAI Jun 09 '20 at 18:51

score -1 · Answer 2 · answered Jun 09 '20 at 17:42

-1

To denote the number of elements in an array, you just do

int arr[N];

Where N represents the number of elements in an array. If you're using a std::vector instead, you would initialize it like this:

vector <int> vec(N);

Then, you can use a for loop to input values into the arrays.

answered Jun 09 '20 at 17:42

Telescope

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"_First line of input file contains a single integer T which denotes the number of test cases_" - That means that `int arr[N];` (or `T`) won't work unless the compiler has a non-standard extension for VLA:s. The standard only permits `int arr[N];` if `N` is `constexpr`. – Ted Lyngmo Jun 09 '20 at 17:46

Denote number of elements in an array with input?

2 Answers2