Python Programming: An Introduction to Computer Science

3.7.EXERCISES 35

int(4.5)
4
int(3.9)
3
long(3.9)
3L
float(int(3.3))
3.0
int(float(3.3))
3
int(float(3))
3

Asyoucansee,convertingtoanintorlongintsimplydiscardsthefractionalpartofa float;thevalueis
truncated,notrounded. Ifyouwanta roundedresult,youcanadd0.5tothevaluebeforeusingint(),
assumingthevalueis positive.
A moregeneralwayofroundingoff numbersis tousethebuilt-inroundfunctionwhichroundsa float
off tothenearestwholevalue.

round(3.14)
3.0
round(-3.14)
-3.0
round(3.5)
4.0
round(-3.5)
-4.0
int(round(-3.14))
-3

Noticethatroundreturnsa float.Thelastexampleshowshow theresultcanthenbeturnedintoanintvalue,
if necessary, byusingint().

3.7 Exercises

1. Show theresultofevaluatingeachexpression.Besurethatthevalueis intheproperformtoindicate
   itstype(int,longint,orfloat).If theexpressionis illegal,explainwhy.

(a)4.0 / 10.0 + 3.5 * 2

(b)10 % 4 + 6 / 2

(c)abs(4 - 20 / 3) ** 3

(d)sqrt(4.5 - 5.0)+ 7 * 3

(e)3 * 10 / 3 + 10 % 3

(f)3L ** 3

2. TranslateeachofthefollowingmathematicalexpressionsintoanequivalentPythonexpression.You
   mayassumethatthemathlibraryhasbeenimported(viaimport math).

(a)

3  4 
 5

(b) nn 2 
^1 

(c) 4 πr^2

(d)  r

cosa
^2  r

sina
^2

(e) xy^22 

yx 11