Pls explain this program(lock and say sequence)

Question

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

int main()
{
char *a = malloc(2), *b = 0, *x, c;
int cnt, len = 1;

for (sprintf(a, "1"); (b = realloc(b, len * 2 + 1)); a = b, b = x) {
puts(x = a);
for (len = 0, cnt = 1; (c = *a); ) {
if (c == *++a)
cnt++;
else if (c) {
len += sprintf(b + len, "%d%c", cnt, c);
cnt = 1;
}
}
}

return 0;
}
Output be like
If input is 5

1
11 //only 1 one in first line
21//two 1 in second line
1211// one 2 and one 1 in third line
111221//one 1 one 2 two 1 in fourth line

Answer 1

That is some crazy awful code you got here ...
The for loop initialize a to "1".
The "condition" for the loop to stop is also used to assign b using realloc
The "iteration" of the for loop is used to assign b to a and x to b (in this order)

the puts will print a value AND assign a to x

Second for loop, initialize len and cnt, use the first character of a as a stopping condition and ... no iteration ...
This for loop will count the number of times a character occur in a string sequence

I have two hypothesis for this code ... either it was made for a code golf or to hurt people. It is not a professional code as its readability is ... awful and so does its maintainability

Do not follow this guy's lead ! (If it is a code golf code and you want to do some yourself, then do not follow what I just said :p )