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carrayspointers
Dariyoush
Dariyoush

Reputation: 508

pointers and 2-D arrays in C

I know how can I use pointers in C with the 1-D array. like the following: but what if we have 2-D arrays? how can I address them by pointers? Thank you. 

#include <stdio.h>

int main() {
  int dar[4] = {1,2,3,4};

  int *sar = NULL;
  sar = dar;
  for (int i = 0; i < 4; i++) {
    printf("%d ", *(sar + i));
    }
}

Upvotes: 2

Views: 98

Answers (3)

Serge Ballesta
Serge Ballesta

Reputation: 148910

A 2-D array is... a 1-D array of 1-D arrays, and you can use the common pointer arithmetics on both.

That means that you can simply do:

#include <stdio.h>

int main() {
  int dar[2][3] = {{1,2,3},
                   {4,5,6}};


  for (int i = 0; i < 2; i++) {
    int *bar = *(dar + i);           // pointer to the row
    for (int j = 0; j < 3; j++) {
      printf("%d ",*(bar+j));        // access the values
     }
     printf("\n");
  }
  printf("\n");
}

It works, because in dar + i, dar decays to a pointer to its first row, so *(dar + 1) (which is *by definition dar[i]) represents the i-th row and in turn decays to a pointer to the first element of that row.

Disclaimer: this is just an addition to JJcopl's answer, but too rich to fit in a comment...

Upvotes: 0

manoliar
manoliar

Reputation: 182

This may also help.

 #include <stdio.h>

int main() 
{   
    int dar[2][3] = {1,2,3,
                    4,5,6}; 
    int index=0;
    for (int line = 0; line < 2; line++) 
    {
        for (int col=0; col<3;col++)
        {               
            printf("%d ", *(dar[0]+index));
            index=index+1;
        }
        printf("\n");
    }   
    return (0);

}

Upvotes: 1

Dariyoush
Dariyoush

Reputation: 508

Thanks to @Qubit I solved the problem. I post the answer for future reference. 

#include <stdio.h>

int main() {
  int dar[2][3] = {{1,2,3},
                   {4,5,6}};

  int *sar = NULL;
  int *bar = NULL;
  sar = dar[0];
  bar = dar[1];

  for (int i = 0; i < 3; i++) {
    printf("%d ", *(sar+i));
   }
  printf("\n");
  for (int j = 0; j < 3; j++) {
    printf("%d ",*(bar+j));
   }

   printf("\n");
}

Upvotes: 0

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