How access with recursion to some element of a struct - c

Question

I would write a function , that elaborates a struct and return the length of an array of character ,that is define in the same struct, in a recursive way.
The struct is:
typedef struct BinSeq {
char* data;
int dimension;
}BinSeq
data, the array of character,can have only two type of character: '0' and '1',while dimension is the length of array, but not of sequence of '0' and '1'.
So I try to write this function:
int length(BinSeq* bin_seq) {
int i;
if(bin_seq->data[i] == '0' || bin_seq->data[i] == '1')
{
i++;
return 1 + length(bin_seq->data[i]);
}else
return 0;
}
but I have may doubts about this. First caused by the compiler that says:
warning: passing argument 1 of ‘length’ makes pointer from integer without a cast [enabled by default]
return 1 + length(bin_seq->data[i]);
^
recursion.c:13:6: note: expected ‘struct BinSeq *’ but argument is of type ‘char’
int length(BinSeq* bin_seq) {
How can I work on the data , If I had to pass to my function the Binseq* bin_seq? I know that my code is in error for this , but if I want calculate the leght I had to increment the variable i, but the it won't , I think, increase. How can I work on this?

Answer 1

like this:
#include <stdio.h>
typedef struct BinSeq {
char *data;
int dimension;
} BinSeq;
int length(BinSeq* bin_seq) {
if(*bin_seq->data == '0' || *bin_seq->data == '1')
return 1 + length(&(BinSeq){bin_seq->data + 1, bin_seq->dimension});
return 0;
}
int main(int argc, char** argv) {
BinSeq binary;
binary.data = "0000110111";
binary.dimension = 2014;
int dimension_of_array = length(&binary);
printf("%d\n", dimension_of_array);
return 0;
}
by using the auxiliary recursive function
int aux_length(const char *data){
if(*data == '0' || *data == '1')
return 1 + aux_length(data + 1);
return 0;
}
int length(BinSeq* bin_seq) {
return aux_length(bin_seq->data);
}

Answer 2

If I interpreted correctly, this code should do what you want:
int length(BinSeq* bin_seq, int i) {
if(bin_seq->data[i] == '0' || bin_seq->data[i] == '1')
{
return 1 + length(bin_seq->data, ++i);
} else {
return 0;
}
}
Although there are more efficient ways to code this: in practice you can simply use pointer arithmetic to loop over the char array until you find anything but a 0 or 1. You have also not shown how you initialize the sequence; one would assume it is done correctly with a known terminator character (e.g. \0).

Answer 3

I had to write a function int length(BinSeq* bin_seq)that calculates recursively the length of the binary sequence bin_seq. The struct is:
typedef struct BinSeq {
char* data;
int dimension;
}BinSeq
and the main is:
int main(int argc, char** argv) {
Binseq* binary;
binary.data = "0000110111";
binary.dimension = 2014;
int dimension_of_array = length(BinSeq* bin_seq);
}
How can I calculate the length of data, if I had to pass bin_seq to function?