All year. While the summer months offer festivals, swimming opportunities in rivers and lakes, crowded and open-air cafes, the winter months offer cozy cafes and nearby clubs and bars.
Zurich is an easy city to walk because it is concentrated in a small area: from the train station to the lake and then to the university on the other side of the river. Public trams are common and prices vary by location (starting from $5 one way).
June is the hottest month with an average maximum value of 19 °C and January is the coldest month with an average maximum value of 0 °C.
People are a little more formal here; Don't take it personally, the only reason for their attitude is Swiss shyness.
Swiss-German
Swiss Franc (CHF)