What happens to a gas's temperature when it is compressed?

When a gas is compressed, its temperature increases. 

Temperature of a system of gases is related to the average kinetic energy of each gas particle in the system. Higher kinetic energy means higher temperature of the system. When a gas is compressed, work is done on the system—that is, on the gas particles. Since energy is conserved in a system, this energy is converted into the kinetic energy of the individual particles. Since this would result to an increase in average kinetic energy of the particles in the system, this is observed as a temperature increase. 

This is different from Charles' law, which states an increase in temperature results in an increase in volume. This law applies when pressure is constant, which is not the case here. Compression of a gas results to an increase in pressure, and this increase in pressure can be translated to an increase in temperature.