## C - Convert array of elements into 2-d matrix

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It might be a stupid question, but I wonder if there is a efficient way to do this.

The situation:

```int* array = malloc(n * m * sizeof(int));
//want to convert array into M[n][m]
```

what I am doing now:

```int** M = malloc(n * sizeof(int*));
for(int i = 0; i < n; i++, array += m)
M[i] = array;
```

I don't think the conversion should be this complex. Is there any simple syntax C provided? Can I declare an `extern M[n][m]` then set its address to the array?

(error handling and memory management in the sample is omitted for simplicity. Just think it as a part of some function.)

After:

```int* array = malloc(n * m * sizeof(int));
```

you can do:

```int (*M)[m] = (int(*)[m])array;
```

and then use `M[1][2]` for example.

You could have done that in the first place too :

```int (*M)[m] = malloc( n * sizeof *M );
```

Two dimensional (2D) arrays in C programming with example, The two dimensional (2D) array in C programming is also known as matrix. This program demonstrates how to store the elements entered by user in a 2d  How to convert a 2-d array of size (m x n) into 1-d array and how to store the element at position [i, j] of 2-d array in 1-d array? Clearly, the size of 1-d array is the number of elements in 2-d array i.e. (m x n). If the elements in the 2-d array are stored in row-major order.

The tricky part is declaring the variable to hold the pointer to the allocated array; the rest is straight-forward — assuming you have a C99 or later compiler.

```#include <stdio.h>
#include <stdlib.h>

static void print_2dvla(int rows, int cols, int data[rows][cols])
{
for (int i = 0; i < rows; i++)
{
printf("%2d: ", i);
for (int j = 0; j < cols; j++)
printf(" %4d", data[i][j]);
putchar('\n');
}
}

int main(void)
{
int m = 10;
int n = 12;

int (*M)[m] = malloc(n * m * sizeof(M[0][0]));
if (M == NULL)
{
fprintf(stderr, "Failed to allocate %zu bytes memory\n", n * m * sizeof(M[0][0]));
exit(EXIT_FAILURE);
}

for (int i = 0; i < n; i++)
{
for (int j = 0; j < m; j++)
M[i][j] = (i + 1) * 100 + (j + 1);
}

print_2dvla(n, m, M);

free(M);
return 0;
}
```

Example output:

``` 0:   101  102  103  104  105  106  107  108  109  110
1:   201  202  203  204  205  206  207  208  209  210
2:   301  302  303  304  305  306  307  308  309  310
3:   401  402  403  404  405  406  407  408  409  410
4:   501  502  503  504  505  506  507  508  509  510
5:   601  602  603  604  605  606  607  608  609  610
6:   701  702  703  704  705  706  707  708  709  710
7:   801  802  803  804  805  806  807  808  809  810
8:   901  902  903  904  905  906  907  908  909  910
9:  1001 1002 1003 1004 1005 1006 1007 1008 1009 1010
10:  1101 1102 1103 1104 1105 1106 1107 1108 1109 1110
11:  1201 1202 1203 1204 1205 1206 1207 1208 1209 1210
```

The key line is:

```int (*M)[m] = malloc(n * m * sizeof(M[0][0]));
```

This says that `M` is a pointer to an array of `int` arrays each of which has the dimension `m`. The rest of the code simply uses that array with the usual 2-subscript notation — `M[i][j]` etc. It can be passed to functions. I've not shown it here, but it is trivial to put the initialization code into a function too, and then have several different sizes of matrix in a single function.

How to take a 1d array and convert the array to a 2d array in a c++ , How do I take a 1d array and convert the array to a 2d array in a c++ function so the You can make an array of arrays (NOT the same as a 2D array) and access elements using the What do you mean by converting an array into a matrix? Get the matrix with most of its elements as 0. Create a new 2D array to store the Sparse Matrix of only 3 columns (Row, Column, Value).; Iterate through the Matrix, and check if an element is non zero.

C - Convert array of elements into 2-d matrix, C - Convert array of elements into 2-d matrix. C - Convert array of elements into 2​-d matrix. It might be a stupid question, but I wonder if there is a efficient way to  Convert the given 2D array into a 1D array. Sort the 1D array; Convert 1D to Spiral matrix; This can be solved by 4 for loops which store all the elements. Every for loop defines a single direction movement along with the matrix.

Use an array of pointers.

```#include <stdio.h>
#include <stdlib.h>

int main()
{
int n = 3, m = 4, i, j, count=0;

int *array[n];
for(i=0; i<n; i++)
array[i] = (int *)malloc(m * sizeof(int));
if( array[i] == NULL)
{
perror("Unable to allocate array");
exit(1);
}

for (i = 0; i < n; i++)
for (j = 0; j < m; j++)
array[i][j] = ++count;

for (i=0; i < n; i++)
for (j=0; j < m; j++)
printf("%d ", array[i][j]);

// free memory

for(i=0; i<n; i++)
free(array[i]);

}
```

Converting one dimensional array to two dimensional array, For example, one matrix can be a submatrix of another; or a one-row or one-​column matrix (a vector) can be the diagonal elements of a square  Write a C program to count total number of even and odd elements in an array. Write a C program to count total number of negative elements in an array. Write a C program to copy all elements from an array to another array. Write a C program to insert an element in an array. Write a C program to delete an element from an array at specified

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Emulating a 2-d array using 1-d array, that no employee feels unfair · How to flatten a Vector of Vectors or 2D Vector in C++ How to convert a 2-d array of size (m x n) into 1-d array and how to store the element at position [i, j] of 2-d array in 1-d array? If the elements in the 2-d array are stored in row-major order. C++ program to emulate 2-d array using. Conversion of a 2D array into 1D array can be of two types : 1. Row wise 2. Column wise Example : 2D array : {1, 2, 3 4, 5, 6 7, 8, 9} 1D array Row wise : {1, 2, 3, 4

C Multidimensional Arrays (2d and 3d Array), In this tutorial, you will learn to work with multidimensional arrays (two-​dimensional and three-dimensional arrays) in C programming with the help of examples. Convert array to arraylist and vice-verse a[2][2], b[2][2], result[2][2]; // Taking input using nested for loop printf("Enter elements of 1st matrix\n"); for (int i = 0; i < 2;  Minimum cost to convert 3 X 3 matrix into magic square; Python | Convert a list of characters into a string; Convert given string so that it holds only distinct characters; Convert characters of a string to opposite case; Check if a given string can be formed using characters of adjacent cells of a Matrix; Maximum perimeter of a square in a 2D grid

• @smac89 in the same way that you'd compute `i + sp * j` for any other variables. When you say `int (*p)[sp]`, that means for a given `i`, `j`, multiply the `j` by `sp` before adding to `i` and using as an offset. All the compiler is doing is converting the manually computed linear offset into a fancy syntax that's easier to read.
• It's feasible to argue that the `int *array = malloc(…);` cannot be a global variable because in C you cannot use the result of a function call to initialize a global (or static) variable.
• You can just use a 2d array and and the elements then, just `array[m][n]` and use a for loop to put the elements into the array. No `malloc` needed