c - Indexes 2d array to 1d -

i want transform 2d array 1d. put important part of code.

int mask[3][3] = {{0, -1, 0}, {-1, 4, -1}, {0, -1, 0}};   (i = 1; < rows - 1; i++) {     (j = 1; j < cols - 1;j++) {         int s;             s = mask[0][0] * image[i-1][j-1]                 + mask[0][1] * image[i-1][j]                 + mask[0][2] * image[i-1][j+1]                  + mask[1][0] * image[i][j-1]                 + mask[1][1] * image[i][j]                 + mask[1][2] * image[i][j+1]                  + mask[2][0] * image[i+1][j-1]                 + mask[2][1] * image[i+1][j]                 + mask[2][2] * image[i+1][j+1];     } } 

my 1d array

for (k = rows + 1; k < (cols * rows) / 2; k++) {   int s;           s =  0 * image_in[k-rows-1]           - 1 * image_in[k-rows]             + 0 * image_in[k-rows+1]            - 1 * image_in[k-1]           + 4 * image_in[k]           - 1 * image_in[k+1]            + 0 * image_in[k+rows-1]           - 1 * image_in[k+rows]           + 0 * image_in[k+rows+1]; }  

that should same don't know if correctly doing transformations. can tell me if ok?

first of all: why want away 2d array? think 2d array dimensions must constant? well, in case have news you: wrong. code should work perfectly:

int width = ..., height = ...; //create 2d array on heap dynamic sizes: int (*image_in)[width] = malloc(height * sizeof(*image_in));  //initialize array for(int = 0; < height; i++) {     for(int j = 0; j < width; j++) {         image_in[i][j] = ...;     } } 

you see, apart cryptic declaration of array pointer, indexing remains same automatic 2d array on stack.

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within given loop, want address cells relative center cell. easiest done addressing relative cell:

for (i = 1; < rows - 1; i++) {     (j = 1; j < cols - 1;j++) {         int* center = &image_in[i][j];         int s = mask[0][0] * center[-width - 1]                 + mask[0][1] * center[-width]                 + mask[0][2] * center[-width + 1]                  + mask[1][0] * center[-1]                 + mask[1][1] * center[0]                 + mask[1][2] * center[1]                  + mask[2][0] * center[width - 1]                 + mask[2][1] * center[width]                 + mask[2][2] * center[width + 1];     } } 

this works because 2d array has same memory layout 1d array (this guaranteed c standard).

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the edge handling in 1d loop wrong: execute body of loop first , last cells of each line. this cannot fixed without introducing if() statements loop slow things down.

this may ignored if consequences proven irrelevant (you still need exclude first , last lines plus cell). however, edge handling easier if stick 2d array.