I wrote a program to swap adjacent element of array using recursion:
static arr_len;
void swap(int *a, int len)
{
int tmp;
if(len == 0 )
return;
else {
swap(a, len-1);
if(len == arr_len-1)
return;
else if (len > 1)
len++;
tmp = a[len];
a[len] = a[len-1];
a[len-1] = tmp;
}
}
int main()
{
int a[] = {1,2,3,4}, i;
arr_len = sizeof(a)/sizeof(a[0]);
swap(a, sizeof(a)/sizeof(a[0]));
for (i = 0; i< 4; i++)
printf("%d\n", a[i]);
}
This seems to work as I see output:
2
1
4
3
But soon I put more element in array as:
int a[] = {1,2,3,4,5,6}
I see this output:
2
1
4
5
6
3
*** stack smashing detected ***: ./a.out terminated
Aborted (core dumped)
For starters using the global variable arr_len is a bad idea.
In any case your function is invalid. Consider a simplified example when the array contains only 1 or 2 elements. When the array contains one element then you are accessing memory beyond the array using an invalid index equal to len in this statement
tmp = a[len];
The function can look much simpler. For example
void swap( int *a, size_t n )
{
if ( !( n < 2 ) )
{
int tmp = a[0];
a[0] = a[1];
a[1] = tmp;
swap( a + 2, n - 2 );
}
}