Arrays in C++ - Reading Assignment

C++ Programming
#361

I’m not an EOS expert, but @thecil might be interested :slight_smile:

Yes primitive types are usually initialized by default when you declare them.

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#362

Besides the Ivan’s explanation, computerphile’s root access via buffer overflow sample is pretty enlightning. Brilliant video channel, full of gems.

#363

PART 1

  1. An array is an aggregate data type that lets us access many variables of the same type through a single identifier.

  2. index[1]

  3. The size of an array can be fixed which means the array length is known at compile time. Or the size of an array can be dynamic which means the array length is not declared and therefore can be changed.

PART 2

  1. We initialize entire arrays via use of an initializer list (which simply means declaring the lists/elements of your arrays inside curly braces and separated by commas). For example:
    int array[5]{ 0, 1, 2, 3, 4 }; // explicitly define the length of the array
    int array[]{ 0, 1, 2, 3, 4 }; // let the initializer list set length of the array

  2. By using sizeof(array)

  3. By dividing the size of the array by the size of the element.

  4. Will result to undefined behavior.

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#364

[quote=“ivan, post:1, topic:3164”]

1. What is an array?
An array is the collection of similar data type, and it is stored in the contiguous memory location.

2. Which index would you use to access the 2nd variable in an array?
First index is 0. The second index is 1. You access the second variable with the index 1 : array[1];

3. What can you say about the size of an array?

// C++ program to find size of an array by using a  
// pointer hack. 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    int  arr[] = {1, 2, 3, 4, 5, 6}; 
    int size = *(&arr + 1) - arr; 
    cout << "Number of elements in arr[] is "
         << size; 
    return 0; 
}`Preformatted text`
  1. How can you initialize an array?
int nums[100] = {0}; // initiallize all values to 0

int nums[5] = {1,2,3,4,5};

// type name[size] = {values};

  1. How can you get the size of an array in bytes?
    12 bytes for array header object (8 bytes for header and 4 bytes for storing length of the array)

  2. How can you use the function sizeof in order to calculate the number of elements in an array?
    sizeof(array) / sizeof(array[0])

  3. What happens when you try to write outside the bounds of the array?
    The computer will overwrite some data that already exist within its memory, to make space for the element that is out of bounds of the array, resulting in undefined behaviour.

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#365

A.

  1. An array is an aggregate data type which allows us to access many variables of the same type through a single identifier.

  2. Index[1]

  3. The size of an array depends on how many variables to allocate(called the array length).

B.

  1. There are many ways to initialize an array in C++ one of them is by using an initializer list like for example:
int prime[5] { 2, 3, 5, 7, 11}; //use initializer list ot initialize the fixed array
  1. By using sizeof()
  2. By dividing the size of the entire array by the size of an array element: sizeof(array)/sizeof(array[0]).
  3. You will get undefined behavior.
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#366

Hello guys!
Maybe someone can help me with this one,

This screenshot below is one of the example on the second article
stdSizefromArticle

and then when I copy the code and run it on my codeblocks
it says it has an error it says ‘size’ is not a member of ‘std’. here is the screenshot below

stdsizearray
stdsizearray711×380 41.8 KB

maybe someone can explain this to me what’s wrong or any explanation
why this thing happen.

Thank you guys in advance. :slight_smile:

#367

size() is fairly new, you must use a compiler code C++17 or higher. You can do this by using a -std=c++17 flag. I’m not sure how you force it in codeblocks.

I’ve done some googling and found this you can try out, hope it helps. :slight_smile:
https://hwdong.net/2020/02/28/Configuring-C++17-supported-compiler-on-wnidows-for-CodeBlocks-or-Visual-studio-code/

1 Like
#368
  1. Data type
  2. index [1]
  3. it can be fixed or not fixed

2nd part

  1. more options, but basically use {} either empty or with added elements
  2. sizeof
  3. sizeof(array) / sizeof(array[0]
  4. we will get undefined behaviour
1 Like
#369

Thank you @Alko89

useOtherCompilerFlagC++
useOtherCompilerFlagC++1159×312 39.9 KB

I tried what you said and now it works! :smiley:
I really appreciate your help.

Have a nice day! :slight_smile:

#370

Reading Assignment: Arrays in C++ (Answers)

pt.1

  1. Array is an aggregate data type that lets you access many variables of the same type through single identifier.
  2. [1]
  3. The size equals the length, its either fixed or dynamic.

pt2.

  1. Via initializer list.
  2. std::size()
  3. It will return the total size of the array( array length multiplied by element size).
  4. You get unidentified behavior.
1 Like
#371

size() gives you the length of the array (number of elements), not the size in bytes. :slight_smile:

1 Like
#372

  1. What is an array?
    Ans: An array is an aggregate data type that lets us access many variables of the same type through a single identifier.

  2. Which index would you use to access the 2nd variable in an array?
    Ans: index of 1.

  3. What can you say about the size of an array?
    Ans: Fixed arrays provide an easy way to allocate and use multiple variables of the same type so long as the length of the array is known at compile time. A second kind of array is known as a dynamic array. The length of a dynamic array can be set at runtime, and their length can be changed.

Part 2

  1. How can you initialize an array?
    Ans: You can initialize entire arrays via use of an initializer list or the less convenient way to
    initialize an array is to do it element by element.

  2. How can you get the size of an array in bytes?
    Ans: size()

  3. How can you use the function sizeof in order to calculate the number of elements in an array?
    Ans: Total size of the array is array length multiplied by element size. sizeof()

  4. What happens when you try to write outside the bounds of the array?
    Ans: When this happens, you will get undefined behavior – For example, it could overwrite the value of another variable, or cause your program to crash.

2 Likes
#373

1a) an array is a data set consisting of 1 type of variable.
2a) i would use [3]
3a) the size of an array is fixed unless using a dynamic array.

1b) To initialize an array, you can either initialize each index individually, or you can use an initalizer list, which consists of all your integer values inside of curly brackets, separated by commas.
2b) use sizeof()
3b) diving the size of an array in bytes by the size of an element in bytes will give you the array length, aka the number of elements in the array.
4) this would cause undefined behavior.

QUESTION: what is the difference between a pointer and an integer? Also, wouldn’t there be a different in size of an integer depending on how big the number is? In the calculations determining array length, the article seemed to assume the same byte amount for all the integers, whether they are 1 digit or two digits.

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#374

You should use 1, array indexes start at 0 so to access the first element you use 0 and the second 1 and so on.

Pointer points to a specific address in memory while an integer is a value stored in memory.

All fundamental types have a fixed size in memory once they are initialize no matter what their value is. Integers are usually 4 bytes. :slight_smile:

#375

oh hmm strange i had a moment of dyslexia there choosing that wrong index # lol. Thanks for the other clarifications!

#376

What is an array?

Array is an aggregate data type that lets us access many variables of the same type through a single identifier.

Which index would you use to access the 2nd variable in an array?

1

What can you say about the size of an array?
it can be either fixed or dynamic.

How can you initialize an array?
can be done it element by element

How can you use the function sizeof in order to calculate the number of elements in an array?
sizeof (array) / sizeof (int)

What happens when you try to write outside the bounds of the array?
undefined behavior

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#377

This will work if its an array of integers, you must also divide by the array element type. A good idea is to divide by the first element in the array because you can be sure it always exists (sizeof(array[0])) :slight_smile:

#378

PART ONE

  1. What is an array? It is an aggregate data type that lets us access many variables of the same type through a single identifier.
  2. Which index would you use to access the 2nd variable in an array? Should remember that execution will start counting from 0. So the second variable is numbered 1. Like array[1]
  3. What can you say about the size of an array? There are two ways to declare an array. One being the dynamic array, where the size is not specified when it is declared and can vary in size. The other being the fixed array, where the size is specified by a compile-time constant on declaration and cannot be changed. The lenght of this array is always +1 the number of single elements.

PART TWO

  1. How can you initialize an array? By assigning element by element (this is the most unconvenient way) or via initializer list. After the declaration should be specified the index and assigned the value.
  2. How can you get the size of an array in bytes? Use the sizeof operator on an array
  3. How can you use the function sizeof in order to calculate the number of elements in an array? array length = sizeof(array) / sizeof(array[0]
  4. What happens when you try to write outside the bounds of the array? This would mean to write in an unallocated memory space and the results are unpredictable.
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#379

I’m not sure if this is accurate. The length of the array is the number of elements in the array but since array indexes start with 0 you will get the final element of the array with the array length - 1 :thinking:

#380

1.1. An array is a collection of variables of the same type. :slight_smile:

1.2. you would use index number 1( array indexing starts from 0)

1.3. you can declare the size of an array when you declare the array or let it be dynamic.

2.1. you initialize an array using curly brackets and add variables using comma int array {1,2,3,4,5}

2.2. you use the sizeof operator on an array

2.3. you divide the result of sizeof(array) with sizeof(element in array) , so you divid the total byte size with the individual element size and by doing this you get the total amount of elements.

2.4. random things can happen. it is undefined behaviour so your program might go crazy.

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