arrange a mix of numbers in an array in alternating +ve & -ve while retaining the order

alternate-merge.c

#include "stdio.h"
#include "stdlib.h"
#define size(x) ({ \
            sizeof(x) / sizeof(int); \
        })

int main(void) {
    int input[] = {4, -10, 2, -2, -7, 3, -3, 5, -4, -5, 1, -9, 0, -6, -1, -8};
    int *i, *neg, *pos;
    int *separators[2];         // pointer to a 2x(not yet know size) array
    
    neg = separators[0] = malloc(sizeof(int) * size(input));
    pos = separators[1] = malloc(sizeof(int) * size(input));
    
    for(i = input; i < input+size(input); i++) {
        if(*i < 0) {        // negative
            *neg++ = *i;
        } else {
            *pos++ = *i;
        }
    }
    
    neg = separators[0];
    pos = separators[1];
    
    i = input;
    int cond1=1, cond2=1;
    
    while(cond1 || cond2) {
        // starting with -ve first
        if (cond1 = (neg < separators[0]+size(separators[0]))) {
            *i++ = *neg++;
        }
        if (cond2 = (pos < separators[1]+size(separators[1]))) {
            *i++ = *pos++;
        }
    }
    
    *i = '\0';
    
    for(i = input; i < input+size(input); i++) {
        printf("%d ", *i);
    }
    
    return 0;
}