CMU 15-112: Fundamentals of Programming and Computer Science
Extra Practice for Unit 3 (Due never) Code Tracing (CT) and Reasoning Over Code (ROC) Exercises

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"))


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?!?"))


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"))


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))


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()


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()

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


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))


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


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