strcat using arrays

#include <stdio.h>

void strcat2(char[], const char[], const char[]);

int main(void)
{
  char a[] = "abc";
  char b[] = "efg";
  char ret[10];

  strcat2(ret, a, b);

  printf("%s\n", ret);

  return 0;
}

void strcat2(char ret[], const char a[], const char b[])
{
  int i=0, j=0;
  while ( (ret[i++]=a[i]) != '\0');
  i--;
  while ( (ret[i++]=b[j++]) != '\0');
  ret[i] = '\0';
}