Member Avatar for 666kennedy

sorry if this a bit of a pain and there are other threads to read about this but can anyone explain how arrays work a bit, i need a quick refresher course.

like how they work, are they like the equivalent of stacks in assembly language? and say you set up an array like

array[20][60]

meaning there are 20 rows of 60 columns?

so how would u change whats stored in each one?

i can expand any of it if i have been vague.

thanks for reading

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Quick clarification and practical tips that build on and without repeating the basics they already covered.

Arrays are just contiguous blocks of memory (C/C++ use row‑major layout for built‑in multi‑dimensional arrays). They are not the same as the CPU stack data structure — a declaration like int a[20][60]; can live on the stack or the heap depending on where/how you declare it, but the array itself is a fixed contiguous region of elements. That contiguous layout is useful: you can operate on an entire 2‑D array as one linear block when the type is a true C array.

To initialize or overwrite the whole 2‑D block without writing nested loops, use algorithms that operate on a range. Example (for a built‑in array):

#include <algorithm>
#include <random>

int a[20][60];

std::mt19937 rng{std::random_device{}()};
std::uniform_int_distribution<int> dist(0, 99);

std::generate(&a[0][0], &a[0][0] + 20*60, [&]{ return dist(rng); });

To replace a single row quickly, use a library call rather than hand loops:

std::fill_n(a[row], 60, 0);   // sets that row to zeros

Notes and cautions:

  • &a[0][0] trick works because built‑in 2‑D arrays are contiguous. std::vector<std::vector<T>> is not contiguous; for that use a flat std::vector<T> sized rows*cols and index with row*cols + col.
  • Large local arrays can overflow the stack — use std::vector (heap) for big buffers.
  • Use std::generate/std::fill/std::copy or memcpy (only for trivially copyable types) for better performance and clearer intent.
  • Prefer <random> engines over rand() for reproducibility and quality.

See the standard algorithm docs for std::generate and std::fill_n for details and overloads: std::generate - cppreference, std::fill_n - cppreference.

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Member Avatar for mrboolf

a one-dimension array is defined by type name[dimension]; or explicitly type name[] = { element1, element2, ... , elementn } where n = dimension. It has exactly n elements, indexed from 0 to n-1. For example, an array of five int would be defined either by int myarray[5]; or by int myarray[] = { 1, 2, 3, 4, 5 } . To access the element you can use array[position] where 0 <= position < dimension of the array. To assign the numbers from 1 to 5 to an array of int you could do

int myarray[5];
myarray[0] = 1;
myarray[1] = 2;
myarray[2] = 3;
myarray[3] = 4;
myarray[4] = 5;

For 2-D arrays the syntax is quite the same: int my2Darray[5][5]; would declare a matrix of 5 rows and 5 columns, and you could access every element exactly like you did with 1-D arrays:

int my2Darray[3][3];
my2Darray[0][0] = 0;
my2Darray[0][1] = 1;
my2Darray[0][2] = 2;
my2Darray[1][0] = 3;
my2Darray[1][1] = 4;
my2Darray[1][2] = 5;
my2Darray[2][0] = 6;
my2Darray[2][1] = 7;
my2Darray[2][2] = 8;

would define the matrix

0 1 2
3 4 5
6 7 8

For N-D arrays you go on like this...

Member Avatar for 666kennedy

i know how to give each one random numbers, if i went

myarray[0][1] = code for random number;
.
.
.
.
.
.
.
myarray[20][60] = code for random number;

is there a way to make all of them random numbers with one or 2 lines of code?

Member Avatar for mrboolf

well you could use loops, something like

for(int i = 0; i < 20; i++) {
     for(int j = 0; j < 60; j++) {
          myarray[i][j] = "code for random number";
     }
}
Member Avatar for vmanes

well you could use loops, something like <snip>

Arrays and loops go together like peanut butter and jelly. Good things separately, great thing together.

commented: lol :-D +1
Member Avatar for 666kennedy

is there a way in 2-D arrays to overwrite or change full rows if array[row][col]

is that the same as the loops from earlier only doing the loop for one dimension?

Member Avatar for vmanes

You will have to do a loop for the row, handling it element by element, just as in a 1D array.

You can write code that handles just the 1D data, and call it for whichever row you want out of the 2D array. Example:

void clear_1D ( int ar[], int size )
{
    int i;
    for( i = 0; i < size; i++ )
        ar[i] = 0;
}

int data[10][20];
//fill the array with some stuff
//now I want row 2 set back to all 0
clear_1D( data[2], 20 );
Member Avatar for mujash.techee

sorry if this a bit of a pain and there are other threads to read about this but can anyone explain how arrays work a bit, i need a quick refresher course.

like how they work, are they like the equivalent of stacks in assembly language? and say you set up an array like

array[20][60]

meaning there are 20 rows of 60 columns?

so how would u change whats stored in each one?

i can expand any of it if i have been vague.

thanks for reading

Hey There ....

Arrays In C++ Are Simple To Understand.
All Ya Gotta Do Is To Conceptualize Arrays
As Rooms Numbered From 0, 1, 2, To X.
These Rooms Ya Call As Data Store Houses.
Now To Access, Retrieve Or Alter Data In Any Room You Would Have To Use The Room Number. For Example, If Room Number 3 Contains 3 People, We Can Access The Data As:

Room[3] = 3;

This Sets The Room 3 To The Value Of 3.

Similarly, Ya Can Access, Retrieve Or Alter The Data In Different Rooms Of An Array.
Once Ya Understand These One Dimensional Arrays ... Two Or Higer Dimensional Arrays Would Be Much Easier To Understand.....

If Ya Need Any More Assistance Please Mail Me At: [email removed]

REGARDS:
MUJASH

Member Avatar for 666kennedy

can you do calculations with individual cells

e.g. like array[1][2] * array[1][3], will that work

Member Avatar for Lerner

Yes, assuming the indexes are valid, that will work.

Member Avatar for mrboolf

I suggest you to read before you ask more questions. Read it carefully and you should be set an gone, and in case of doubt come back here for help.

Just a tip about

For Example, If Room Number 3 Contains 3 People, We Can Access The Data As:

Room[3] = 3;

This Sets The Room 3 To The Value Of 3.

: remember that Room Number 3 is the Fourth Room of your Hotel :)

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