0

I would like to select an array with a variable in order to copy its values into another array.

I'm struggling with this line : xyz[i] = arr1[i];

I want to replace arr1 with the variable name

Something like I use in Bash : xyz[i] = ${name}[i];

Does anyone have any clues or solutions ?

Here's a simplified version of my code

#include <stdio.h>

int main() {
    int arr1[8] = {1, 2, 3, 4, 5, 6, 7, 8};
    int arr2[8] = {8, 7, 6, 5, 4, 3, 2, 1};

    int xyz [8], i, num=8;
    int loop;
    char name[4];


    printf("Array's name ? ");
    scanf("%s", &name);

    // Array's name ? arr1

    for (i = 0; i < num; i++) {
        xyz[i] = arr1[i];
    }

    for(loop = 0; loop < 8; loop++) {
        printf("%d ", xyz[loop]);
    }

    // 1 2 3 4 5 6 7 8

   return 0;
}
Improve this question
3
  • 4
    variable names dont exist at runtime. If you want to map names to objects you have to provide the mapping yourself Commented Jan 8, 2020 at 15:26
  • "I'm struggling with this line" Why? What error do you get? "I'm struggling" is not a problem description. Commented Jan 8, 2020 at 15:31
  • 1
    @underscore_d there is no error. OP does explain what they want to do, and there is a good excuse for having no idea how or not showing an attempt: It isnt possible ;) Commented Jan 8, 2020 at 15:36

2 Answers 2

Reset to default
1

C doesn't provide this capability (after the source code has been compiled, variable names no longer exist as such). You'll need to use a pointer to do something like this, and you'll need to add logic to assign the right value to that pointer. For a couple of names, a simple if/else statement is good enough:

int *p = NULL;   // p will point to the first element of arr1 or arr2 depending on the value of name

if ( strcmp( name, "arr1" ) == 0 )
  p = arr1;
else if ( strcmp( name, "arr2" ) == 0 )
  p = arr2;
else
  fprintf( stderr, "%s is not a valid name\n", name );

if ( !p )
{
  // handle bad entry
}
else
{
  for ( i = 0; i < num; i++ )
    xyz[i] = p[i];
}

In the general case (where you have more than just a few options), you'll want to build some kind of a map that associates a name with an address:

struct {
  char *name;
  int *arr;
} name_arr_map[] = { 
  {"arr1", arr1}, 
  {"arr2", arr2}, 
  ... 
};

int *p = NULL;

// get name

for ( i = 0; i < N; i++ ) // N entries in our map
{
  if ( strcmp( name_arr_map[i].name, name ) == 0 )
  {
    p = name_arr_map[i].arr;
    break;
  }
}

if ( !p )
{
  // handle bad entry
}
else
{
  for ( i = 0; i < num; i++ )
    xyz[i] = p[i];
}

For a few entries (a couple of dozen or so) a simple linear search like this is good enough. If you have more than that, you may want to use a more sophisticated structure like a hash table or a tree.

However, for this specific case...

When you find yourself creating multiple variables of the same type with the names thing1, thing2, etc., that's a real strong hint you want an array - in this case, a 2D array:

int arrs[2][8] = { { 1, 2, 3, 4, 5, 6, 7, 8 },
                   { 8, 7, 6, 5, 4, 3, 2, 1 } };

In this case you don't need a name, just an index:

int idx = 0;
...
printf( "Which array do you want to use, 0 or 1? " );
scanf( "%d", &idx );
if ( idx < 0 || idx > 1 )
{
  // handle bad entry
}
else
{
  for ( i = 0; i < 8; i++ )
    xyz[i] = arrs[idx][i];
}
Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

0

C does not have the ability to do this. You can either manually do it with if/else statements or find some sort of hashmap implementation in c like this one in order to map from names to arrays. Note that C++ has a pre-installed hashmap implementation that you don't have to download.

Improve this answer

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.