I want after I do some calculation create an array in C would u please help me?
int len_arr = (sizeof inputs)/(sizeof inputs[0]);
int half_arr = len_arr / 2;
if(len_arr%2 != 0)
half_arr++;
int m[half_arr][half_arr];
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3 Answers
I'm assuming you wish to create a matrix with row/column size of half_arr.
int i;
int len_arr = (sizeof inputs)/(sizeof inputs[0]);
int half_arr = len_arr / 2;
if(len_arr%2 != 0)
half_arr++;
int **m = malloc(half_arr * sizeof(int));
for (i = 0; i < half_arr; i++)
*m = malloc(half_arr * sizeof(int));
You should then be able to access m using m[row][column] or m[column][row].
7 Comments
BlackBear
then he has to do another loop like that freeing all that memory
James
@BlackBear: Yes, he does. If he wishes to use
m[][] syntax though it is needed.
Jeff Mercado
int m** that a new type? :)
Amir
Compiling... main.c C:\OBA_VTS\SVD_Enhancement\main.c(25) : error C2143: syntax error : missing ';' before 'type' C:\OBA_VTS\SVD_Enhancement\main.c(28) : error C2065: 'm' : undeclared identifier C:\OBA_VTS\SVD_Enhancement\main.c(28) : error C2100: illegal indirection C:\OBA_VTS\SVD_Enhancement\main.c(28) : warning C4013: 'malloc' undefined; assuming extern returning int C:\OBA_VTS\SVD_Enhancement\main.c(46) : error C2109: subscript requires array or pointer type
Christoph
@James: no, it's not - the C language supports variable-length arrays; if rima uses MSVC as a compiler (which basically only supports C90), I strongly suggest using C++ instead or switching to MinGW
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You need to use malloc to allocate your 2-dimensional array.
Look at this LINK for a good explanation.
EDIT:
Starting from the code at the given link, I've written a piece of code that should work.
Some differences from James' code:
- declaration of
mat the top of the code block - conversion from the return type of malloc (void *) to the correct one
- memory deallocation at the end
- it's a complete code, that must work :P
#include <stdlib.h>
int main ()
{
// just an example of inputs...
int inputs[3][7];
// your code
int i;
int **m;
int len_arr = (sizeof inputs)/(sizeof inputs[0]);
int half_arr = len_arr / 2;
if(len_arr%2 != 0)
half_arr++;
// allocation of the array
m = (int **)malloc(half_arr * sizeof(int *));
for(i = 0; i < half_arr; i++)
m[i] = (int *)malloc(half_arr * sizeof(int));
// use the array as you like...
// ...
// let's release the allocated memory properly
for(i = 0; i < half_arr; i++)
free(m[i]);
free(m);
}
Your code is valid C99. You might want to use a compiler which supports newer revisions of the C language.
On Windows, I'd go with the MinGW edition of gcc. If you're stuck with MSVC, I suggest using C++ instead: the standard container types will make your life less painful.
