Array of pointers

[Tubs]

Is the best way to change a array belonging to the main function inside a different function by using enumerated types & a pointer to it?

[wtd]

Well, you have an array declared inside your main function.

c:

int main() {    int foo[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};    return 0; }

What you really have is a glorified pointer that points to the beginning of the array.

This pointer can be passed to another function. But, since you just have a glorified pointer, no information about the length of the array gets passed with it. So we have a separate parameter for the length of the array.

Then inside the function, we can iterate over the array.

c:

void increment_all(int *input_array, int size_of_array) {    int index;    for (index = 0; index < size_of_array; index++)    {       input_array[index]++;    } }

And back in main we can use that.

c:

#include <stdio.h> void increment_all(int *input_array, int size_of_array) {    int index;    for (index = 0; index < size_of_array; index++)    {       input_array[index]++;    } } int main() {    int index;    int foo[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10};    increment_all(foo, 10);    for (index = 0; index < 10; index++)    {       printf("%d\n", foo[index]);    }    return 0; }

[Tubs]

I should have been more specific. How about multi dementional arrays? (2 in the case I am working with)

[wtd]

Ok. A two-dimensional array is an array of arrays. Each of those arrays is a pointer to its beginning. Thus the two-dimensional array is just a glorified pointer to a glorified pointer.

However, there is a complication. If we have a multidimensional array, we cannot pass declare the function as taking a pointer to a pointer.

Here's some working code to consider:

c:

#include <stdio.h> void increment_all(int (*input_array)[5], int y_dimension) {    int x_index, y_index;    for (y_index = 0; y_index < y_dimension; y_index++)    {       for (x_index = 0; x_index < 5; x_index++)       {          input_array[y_index][x_index]++;       }    } } int main() {    int x_index, y_index;    int foo[2][5] = {{1, 2, 3, 4, 5}, {6, 7, 8, 9, 10}};    increment_all(foo, 2);    for (y_index = 0; y_index < 2; y_index++)    {       for (x_index = 0; x_index < 5; x_index++)       {          printf("%d\n", foo[y_index][x_index]);       }    }    return 0; }

[Tubs]

Isn't C silly. You rock my socks wtd.

[wtd]

Tubs wrote:

Isn't C silly.

Yes.

Tubs wrote:

You rock my socks wtd.

Glad to help.

Thank you for asking a relatively focused question. These are so much easier to approach than, "here's my hundred lines of code... what's wrong?!"

[wtd]

Yes, C is silly. Fortunately there are other fish in the sea.

code:

# let foo = [|[|1; 2; 3|]; [|4; 5; 6; 7|]|];; val foo : int array array = [|[|1; 2; 3|]; [|4; 5; 6; 7|]|] # let increment_all arr =      for y = 0 to Array.length arr - 1 do         for x = 0 to Array.length arr.(y) - 1 do            arr.(y).(x) <- arr.(y).(x) + 1         done      done;; val increment_all : int array array -> unit = <fun> # increment_all foo;; - : unit = () # foo;; - : int array array = [|[|2; 3; 4|]; [|5; 6; 7; 8|]|]

[Tubs]

*backs away slowly towards the door*

*runs*

[wtd]

Here's just the function:

code:

let increment_all arr =    for y = 0 to Array.length arr - 1 do       for x = 0 to Array.length arr.(y) - 1 do          arr.(y).(x) <- arr.(y).(x) + 1       done    done

That isn't so bad, is it?

[Tubs]

Not trying to be a nuisance and post my 100 line program and ask why its not working, but I really don't know how to solve this problem. Since this program uses reading / writing from .txt files it crashes inside my IDE, but says that there are no errors. However, when i try to run the .exe that has a windows error as well so I am left with absolutely no idea on what is failing (I suspect it has something to do with the borders of the array). The .txt file is a 25x25 square of X's, with -'s along the border.

dev c++

code:

#include <stdio.h> #define ROWS 25 #define COLS 25 void generate(char (*grid)[25], int y_dim); int main(int argc, char *argv[]) { int x, y, k, j, rep; char cells[ROWS][COLS], i; FILE *in;         //Pointers to open and close the file in = fopen( "data.txt", "r" );    // open a file for reading for(y = 0; y < 25; ++y) {     for(x = 0; x < 25; ++x)         {         fscanf(in, "%c", &cells[x][y] );         } } fclose (in); for (k = 0; k < COLS; ++k)       {       printf ("%c", cells[j][k]);       } printf ("Enter 1 to generate again> "); scanf ("%d", &rep); if (rep == 1) { rep = 0; do {   generate(cells, COLS - 1);   for (j = 0; j < ROWS; ++j)     {     for (k = 0; k < COLS; ++k)       {       printf ("%c", cells[j][k]);       }   printf ("\n");      } printf ("Enter 1 to generate again> "); scanf ("%d", &rep); } while (rep = 1); } system ("pause");   return 0; } void generate(char *grid[25], int y_dim) {    int x_i, y_i, friends = 0;    for (y_i = 1; y_i < y_dim; y_i++)    {       for (x_i = 1; x_i < 24; x_i++)       {         if (grid[y_i - 1][x_i - 1] == 'O')           friends++;         if (grid[y_i - 1][x_i] == 'O')           friends++;         if (grid[y_i - 1][x_i + 1] == 'O')           friends++;         if (grid[y_i][x_i - 1] == 'O')           friends++;         if (grid[y_i][x_i + 1] == 'O')           friends++;         if (grid[y_i + 1][x_i - 1] == 'O')           friends++;         if (grid[y_i + 1][x_i] == 'O')           friends++;         if (grid[y_i + 1][x_i + 1] == 'O')           friends++;        /// Conditions         if (grid[y_i][x_i] == 'O')           // no survival code due to no changes           if (friends >= 4 || friends < 2)  // death              grid[y_i][x_i] = 'X';         if (grid[y_i][x_i] == 'X')           if (friends = 3)   // birth             grid[y_i][x_i] == 'O';       }    } }

[Tubs]

OH ya this is the game of life. If that helps.

[wtd]

Amazingly enough, well-formatted code is easier to work with.

[Tubs]

Whats wrong with that?

[wtd]

c:

#include <stdio.h> #define ROWS 25 #define COLS 25 void generate(char (*grid)[25], int y_dim); int main(int argc, char *argv[]) {    int x, y, k, j, rep;    char cells[ROWS][COLS], i;    FILE *in;         //Pointers to open and close the file    in = fopen("data.txt", "r");    // open a file for reading    for (y = 0; y < 25; ++y)    {       for (x = 0; x < 25; ++x)       {          fscanf(in, "%c", &cells[x][y]);       }    }    fclose (in);    for (k = 0; k < COLS; ++k)    {       printf("%c", cells[j][k]);    }    printf("Enter 1 to generate again> ");    scanf("%d", &rep);    if (rep == 1)    {       rep = 0;       do       {          generate(cells, COLS - 1);          for (j = 0; j < ROWS; ++j)          {             for (k = 0; k < COLS; ++k)             {                printf("%c", cells[j][k]);             }             printf("\n");          }          printf("Enter 1 to generate again> ");          scanf("%d", &rep);       } while (rep = 1);    }    system ("pause");    return 0; } void generate(char *grid[25], int y_dim) {    int x_i, y_i, friends = 0;    for (y_i = 1; y_i < y_dim; y_i++)    {       for (x_i = 1; x_i < 24; x_i++)       {         if (grid[y_i - 1][x_i - 1] == 'O')           friends++;         if (grid[y_i - 1][x_i] == 'O')           friends++;         if (grid[y_i - 1][x_i + 1] == 'O')           friends++;         if (grid[y_i][x_i - 1] == 'O')           friends++;         if (grid[y_i][x_i + 1] == 'O')           friends++;         if (grid[y_i + 1][x_i - 1] == 'O')           friends++;         if (grid[y_i + 1][x_i] == 'O')           friends++;         if (grid[y_i + 1][x_i + 1] == 'O')           friends++;        /// Conditions         if (grid[y_i][x_i] == 'O')           // no survival code due to no changes         if (friends >= 4 || friends < 2)  // death            grid[y_i][x_i] = 'X';         if (grid[y_i][x_i] == 'X')            if (friends = 3)   // birth               grid[y_i][x_i] == 'O';       }    } }

[Tubs]

I dont know how to do super cool stuff like that