Getting a nice clean cut is important on both cables and housing to stop them fraying etc. There is a method I have used which works well when you dont have cable cutters nearby (ie on a trail miles from home). You need 1) a sharp knife (like on those multi-tools, not a kitchen knife etc), 2)something firm to put the cable/housing on - good piece of dead wood or a rock that wont shatter, 3) something to strike the blade of the knife with - another rock. 2 can be subsituted for a hard bench or even a flat piece of steel. 3 can be substituted for a hammer. Place the blade over the cable/housing on the hard surface and whack it hard with the hammer in a single go.