Extra Practice for Unit 3 (Due never) Code Tracing (CT) and Reasoning Over Code (ROC) Exercises

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These problems will help you prepare for hw3 and quiz3. They are optional and you are encouraged to collaborate when working on them.

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Code Tracing (CT)
What will each of these print?

1. def ct1(s, t):
       result = ""
       for c in  s:
           if (c.upper() not in  "NO!!!"):
               i = t.find(c)
               if (result != ""): result += ":"
               result += "%d%s%s%s" % (i, c, s[i], t[i])
       return result
   print(ct1("net", "two"))

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2. def ct2(s):
       result = ""
       d = ord("a")
       for c in s.lower():
           if  (c.isalpha() and (ord(c) >= d)):
               result += str(ord(c) - d) + chr(d)
               d += 1
       return result
   print(ct2("Be a CA?!?"))

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3. def ct3(s):
       result = ""
       while (len(s) > 1):
           result += s[:1] + s[2:4] + "."
           s = s[1:-1:2]
       return result + s
   print(ct3("abcdefghi"))

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4. def ct4(s,  n):
       result = ""
       d = 0
       while (n > 0) and (len(s) > 0):
           if (s[-1].isdigit()):
               result += str((n%10)%int(s[-1]))
           else:
               result += chr(ord('D')+d)
           n //= 10
           s = s[1:-1]
           d += 1
       return result
   print(ct4("abc3c3", 2468))

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5. # Graphics-CT #1
   # Draw a picture on a piece of paper showing what this draws when it runs.
   
   import basic_graphics
   
   def draw(canvas, width, height):
       # assume (width,height) == (300,300)
       canvas.create_rectangle(10, 10, width-10, height-10, fill=None)
       (cx, cy, d) = (width*2/3, height/3, width/10)
       L = [ ]
       for i in range(-2,3):
           (dx, dy, r) = (cx+d*i, cy+abs(d*i), d/2)
           canvas.create_line(dx, dy, cx, cy+100)
           canvas.create_oval(dx-r, dy-r, dx+r, dy+r, fill="gray")
           L.append((dx, 30+10*i**2))
       canvas.create_polygon(L, fill="gray")
       (x0, y0, x1, y1) = (20, 20, 100, 200)
       canvas.create_rectangle(x0, y0, x1, y1, fill="gray")
       canvas.create_oval(x0, y0, x1, y1, fill="white")
       textY = height-60
       canvas.create_line(20, textY, width-20, textY)
       canvas.create_text(width/2, textY, text="CT1",
                          font="Arial 16", anchor="s")
       canvas.create_text(width/2, textY, text="(What will this draw?)",
                          font="Arial 16", anchor="n")
   
   basic_graphics.run()

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6. # Graphics-CT #2
   # Draw a picture on a piece of paper showing what this draws when it runs.
   
   import basic_graphics
   
   def draw(canvas, width, height):
       (x1,y1) = (200,0)
       for x in range(50,500,200):
           for y in range(x, 400, 150):
               canvas.create_line(x,y,x1,y1)
               canvas.create_text(x,y,text=str((x,y)))
               (x1,y1) = (x,y)
   
   basic_graphics.run()

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Reasoning Over Code (ROC)
Find values for the parameters so the functons return True:

1. def rc1(n):
       assert(type(n) == int)
       s = str(n)
       return ((2000>n>1000) and (n == int(s[0]*len(s))))

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2. def rc2(s, t,  n):
       q = ""
       for i in range(len(s)):
           q += t[(i+n)%len(t)]
       print(q)
       return ((len(s) == 2*len(t)) and
               (not s.startswith(t)) and
               (q == s))

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3. import string
   
   def rc3(n,k,x):
       s = "ab\tc\\d"
       assert(len(s) == n)
       assert(s[k] in string.whitespace)
       assert(s.find("b") == s.find("e") + x)
       return True

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4. def rc4(s):
       assert (s[0] == "d" and len(s) == 5)
       for i in range(1, len(s)):
           if (ord(s[i]) != (i + ord(s[i-1]))): #1 + d
               return False
       return True

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