Looping through multiple arrays in C.

Applications Programming
1

Not sure if this is possible, but I've tried this about a thousand ways now. I am making something with a lot of arrays. I thought I could put the array names into a separate array and then loop through them to call all of their elements. This is the best I've got so far:

#include <stdio.h>
#include <stdlib.h>

int main() {

	char c;

	int a [5] = {1,2,3,4,5};
	int b [5] = {6,7,8,9,10};

	for(c = 'a'; c <= 'b'; ++c) {
		for (int j = 0; j < 5; j++){
			printf("%d\n", c[j]);
		}
	}
}

From it I get the following error:

$ gcc canloop.c -o canloop
canloop.c: In function �main':
canloop.c:17:20: error: subscripted value is neither array nor pointer nor vector
    printf("%d\n", c[j]);

Oddly enough it still runs despite the error:

$ ./canloop 
0
1
2
3
4
0
1
2
3
4

Seems its not incrementing on the first loop with c. I've tried changing ++c to c++, casting, etc, but no change. Anyone know if this is not possible, some way to do this better or what I may be missing?

1 Like
2

Did you consider making c a pointer to int array?

1 Like
3

I did try that with pointers several different ways. Just tried it again and for the first time this compiled with no errors:

#include <stdio.h>
#include <stdlib.h>

int main() {

    int c;
    int *test;
    test = &c;

    int a [5] = {1,2,3,4,5};
    int b [5] = {6,7,8,9,10};

    for(c = 'a'; c <= 'b'; ++c) {
        for (int j = 0; j < 5; j++){
            printf("%d\n", test[j]);
        }
    }
}

The output is uniq, but wrong:

$ ./canloop
97
757351276
32767
0
4
98
757351276
32767
0
4

I guess I'm not dereferencing it right? Maybe I've just been up too long, but I'm open to more suggestions.

4

That it compiled without errors only means your program is correct grammatically, the same way "my hovercraft is full of eels" will pass a grammar check but not help Belgians communicate with foreigners. Your program does not do what you think it does.

for(c = 'a'; c <= 'b'; ++c)

'a' and 'b' are the ASCII integers 91 and 92, respectively. They are not the arrays a and b and cannot be used to retrieve those variables.

How about this?

#include <stdio.h>

int main(int argc, char *argv[])
{
        int a [5] = {1,2,3,4,5};
        int b [5] = {6,7,8,9,10};
        int *c[]={a, b}; // c[0] is effectively a, c[1] is effectively b

        int n, m;

        for(n=0; n<1; n++)
        {
                for(m=0; m<5; m++)
                {
                        printf("Array %d[%d] = %d\n", n, m, c[n][m]);
                }
        }
}
3 Likes
5

I will agree with what you said. I knew it was a logical error instead of syntactical one when I saw it. I was just happy to have made any progress at that point.

Your code is much better and cleaner, but I did have to edit it. At first it only printed the first array:

$ ./canloop 
Array 0[0] = 1
Array 0[1] = 2
Array 0[2] = 3
Array 0[3] = 4
Array 0[4] = 5

I changed 'for(n=0; n<1; n++)' to 'for(n=0; n<2; n++)' and both arrays printed correctly:

 $ ./canloop 
Array 0[0] = 1
Array 0[1] = 2
Array 0[2] = 3
Array 0[3] = 4
Array 0[4] = 5
Array 1[0] = 6
Array 1[1] = 7
Array 1[2] = 8
Array 1[3] = 9
Array 1[4] = 10

Much appreciated!

1 Like