Print with long-edge double-sided option.

/usr/bin/lpr -P -o Duplex=DuplexNoTumble

Combine multiple pdfs into one pdf

gs -dNOPAUSE -sDEVICE=pdfwrite -sOUTPUTFILE=chem120_assnt1.pdf -dBATCH ./1638_001.pdf ./1638_002.pdf ./1638_003.pdf ./1638_004.pdf ./1638_005.pdf ./1638_006.pdf ./1638_007.pdf ./1638_008.pdf ./1638_009.pdf ./1638_010.pdf ./1638_011.pdf ./1638_012.pdf ./1638_013.pdf ./1638_014.pdf ./1638_015.pdf ./1638_016.pdf

Advantage of Const Reference over Const Pointer
- It eliminates any question of memory ownership.
- It is Non-NULL.