in desert, climate is hot while in hilly areas climate is cold why?
 

It is necessary that the climate of desert always be hot and that of the hilly areas always cold. Example: Ladakh is an example of a cold desert whereas Sahara desert is and extremely hot desert. 
Factors affecting climate: 

• Global positioning: The geographical positioning of a place on globe is defined by latitudes and longitudes. In relation to latitudes and longitudes, there are three horizontal dividers of earth namely; tropic of cancer, tropic of Capricorn and equator. 
• Areas falling in the between the two tropical lines have tropical climates. The equator divides the earth in southern and northern regions. Places near equator has hot and humid climate whereas places near Polar Regions have cold and dry climate. 
• Altitudes: High altitudes have colder climates as compared areas falling in low altitudes. Cold deserts are at a considerable height from the sea level. 
• Atmospheric conditions: Pressure and Winds along with temperature are important atmospheric conditions that plays a deciding factor for climatic and weather conditions:
  1.  Pressure and surface winds.
  2.  Upper air circulation.
  3.  Western cyclonic disturbances and tropical cyclones.a