Loop Patterns

Most pseudocode output questions are loop-pattern questions.

FOR loop

FOR i = 1 TO 5
    DISPLAY i
END FOR

Output:

1 2 3 4 5

If loop includes both ends, count is:

end - start + 1

FOR loop with step

FOR i = 2 TO 10 STEP 2
    DISPLAY i
END FOR

Output:

2 4 6 8 10

Reverse loop

FOR i = 5 DOWNTO 1
    DISPLAY i
END FOR

Output:

5 4 3 2 1

WHILE loop

Condition checked before loop body.

SET i = 1
WHILE i <= 3
    DISPLAY i
    SET i = i + 1
END WHILE

Output:

1 2 3

REPEAT UNTIL loop

Body executes first. Condition checked later.

SET i = 5
REPEAT
    DISPLAY i
    SET i = i + 1
UNTIL i > 5

Output:

5

Nested loop count

FOR i = 1 TO 3
    FOR j = 1 TO 2
        DISPLAY i, j
    END FOR
END FOR

Inner loop runs 2 times for each i.

Total output lines:

3 × 2 = 6

Pattern printing

Triangle

FOR i = 1 TO 4
    FOR j = 1 TO i
        DISPLAY "*"
    END FOR
    DISPLAY newline
END FOR

Output:

*
**
***
****

Number of stars:

1 + 2 + 3 + 4 = 10

Common loop output patterns

Pattern	Code idea	Output idea
Sum 1 to n	sum = sum + i	n(n+1)/2
Factorial	fact = fact * i	n!
Count digits	divide by 10	number of digits
Reverse number	rev = rev*10 + digit	reversed digits
Multiplication table	n*i	table values
Nested count	outer × inner	total iterations

Off-by-one examples

FOR i = 1 TO 5

Runs 5 times.

WHILE i < 5

If i starts at 1, runs for i=1,2,3,4 = 4 times.

WHILE i <= 5

If i starts at 1, runs for i=1,2,3,4,5 = 5 times.