Hi learningunix,
the line checks if the left-most byte of 'num' is '1'.
'&num' is a pointer to the memory address where the first byte of 'num' resides. The '(char*)' casts this pointer '&num' (which is a pointer to int) to a pointer to char. Since char is a one byte data type accessing that 'pointer to char' with '*' accesses the first byte of the int. In little endian this byte has to be '1' for and 'int' which is '1' - in big endian the first byte would be '0' since the least significant byte is the most right one ...
Hope that helps,
ZOPPO
