Answer to Question #320435 in Algorithms for NTANGA

Question

1. Determine the exact output that is produced when the following code is executed. (7)

for x = 1 to 10 step 1

for y = 1 to x step 1

if y MOD 2 = 0 AND x MOD 2 <> 0 || y MOD 2 <> 0 AND x MOD 2 = 0 then

display "*"

else

display "#"

endif

next y

display " " ~newline

next x

2. Rewrite the following for-loop as a pre-test while-loop. (6)

for x = 1 to 10

for y = 10 to x

if y MOD 2 = 0 then

display "*"

else

display "#"

endif

display " " ~newline

3. Rewrite the following for-loop as a post-test do-loop. (5)

for x = 20 to -20 step -3

display "x = ", x

next x

4. Identify an error in the following pseudocode: (2)

sum = 0

for x = 1 to 10

if y MOD 2 = 0

display y

sum = sum + y

Answer 1

1

#
*#
#*#
*#*#
#*#*#
*#*#*#
#*#*#*#
*#*#*#*#
#*#*#*#*#
*#*#*#*#*#

2.

x = 1
while x <= 10
    y = 10
    while y >= x
        if y MOD 2 = 0 then
            display "*"
        else
            display "#"
        endif
        y = y - 1
    display " " ~newline
    x = x + 1

3.

x = 20
do
    display "x = ", x
    x = x - 3
while x > -20

4.

sum = 0

for x = 1 to 10
    if y MOD 2 = 0
        display y
    sum = sum + y

The wrong variable is used inside the loop.

Correct algorithm:

sum = 0

for x = 1 to 10
    if x MOD 2 = 0
        display x
    sum = sum + x