Setting up the variable columns of a trace table

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Quick Questions

Shade in the A or B circle for each question.

1. How many columns does a trace table need for the variables Total, Count and Average?

A One column only, shared by all three variables

B One column for each variable: three columns

2. In what order should the variable columns be placed in a trace table?

A The order the variables first appear in the algorithm

B Alphabetical order of the variable names

3. An algorithm has DECLARE Num : INTEGER and DECLARE Total : INTEGER. What goes in the column headings?

A Num and Total

B INTEGER and INTEGER

4. A FOR loop uses the counter variable i. Should the trace table include a column for i?

A Yes, the loop counter is a variable and needs its own column

B No, loop counters are handled by the loop so they are left out

5. A new row is made and Total does not change in that step. What should you put in the Total cell?

A Write 0 in the cell

B Leave the cell blank

Match the Pairs

Draw a line connecting each item on the left to its match on the right.

Left column		Right column
1DECLARE Total : INTEGER		ADECLARE Num : INTEGER DECLARE Sum : INTEGER DECLARE Count : INTEGER
2FOR Count ← 1 TO 4		BTotal needs its own column in the trace table, placed in the order the variable first appears
3Variables are listed as columns in the order they first appear in the algorithm		CSum ← 0
4A starting value is entered in the first row of the variable's column		DCount and Num have no columns. Each variable must have its own column.
5A trace table with only one column, Total, for an algorithm that declares Total, Count and Num		EThe loop counter Count also gets its own column, and its value changes on each pass of the loop
6Row 1: Count = 1, Total = 5 Row 2: Count = 1, Total = 5 (Count repeated)		FCount is written again even though it did not change. The cell should be left blank.

Definitions

one column per variable

Fill in the Blanks

Complete each line of code by filling in the missing parts.

DECLARE Total : INTEGER DECLARE Count : INTEGER Columns: Total | _____ | OUTPUT

FOR Num ← 1 TO 3 Total ← Total + Num Columns: ___ | Total | OUTPUT

_______ Score : INTEGER // Score gets its own trace table column

DECLARE Total : INTEGER _____ ← 0 // The Total column starts at 0

Count ← Count + 1 // Total unchanged: leave its cell _____

Spot the Error

Shade in the letter of the line that contains an error.

Question 1

A DECLARE Total : INTEGER

B DECLARE Count : INTEGER

C Total = 0

D Count ← 0

Question 2

A DECLARE Num : INTEGER

B DECLARE Total : INTEGER

C Total ← 0

D FOR Count = 1 TO 3

E INPUT Num

F NEXT Count

Question 3

A // Total ← 0 then Num ← 4

B Num | Total | OUTPUT

C 0 | |

D | 4 |

Question 4

A DECLARE Score : INTEGER

B DECLARE Name STRING

C INPUT Name

D INPUT Score

Question 5

A // Count ← 1, OUTPUT Count

B Count | OUTPUT

C 1 |

D 1 | 1

Answer Key

Setting up the variable columns of a trace table

Section A: Quick Questions

B — One column for each variable: three columns

A — The order the variables first appear in the algorithm

A — Num and Total

A — Yes, the loop counter is a variable and needs its own column

B — Leave the cell blank

Section B: Match the Pairs

DECLARE Total : INTEGER → Total needs its own column in the trace table, placed in the order the variable first appears

FOR Count ← 1 TO 4 → The loop counter Count also gets its own column, and its value changes on each pass of the loop

Variables are listed as columns in the order they first appear in the algorithm → DECLARE Num : INTEGER DECLARE Sum : INTEGER DECLARE Count : INTEGER

A starting value is entered in the first row of the variable's column → Sum ← 0

A trace table with only one column, Total, for an algorithm that declares Total, Count and Num → Count and Num have no columns. Each variable must have its own column.

Row 1: Count = 1, Total = 5 Row 2: Count = 1, Total = 5 (Count repeated) → Count is written again even though it did not change. The cell should be left blank.

Section C: Definitions

one column per variable — To set up a trace table, give each variable its own column in the order they first appear, then add a row each time a value changes. Leave unchanged cells blank.

Section D: Fill in the Blanks

DECLARE Total : INTEGER
DECLARE Count : INTEGER
Columns: Total | Count | OUTPUT

FOR Num ← 1 TO 3
   Total ← Total + Num
Columns: Num | Total | OUTPUT

DECLARE Score : INTEGER
// Score gets its own trace table column

DECLARE Total : INTEGER
Total ← 0
// The Total column starts at 0

Count ← Count + 1
// Total unchanged: leave its cell blank

Section E: Spot the Error

C — Assignment uses ←, not =. In Cambridge pseudocode = is a comparison. Total ← 0 sets the starting value, which goes in the first row of the Total column.

D — A FOR loop sets its counter with ←, so it should be FOR Count ← 1 TO 3. The loop counter Count gets its own column in the trace table, and its starting value 1 goes in the first row.

B — Columns go in the order the variables first appear in the algorithm. Total is set before Num, so the header should be Total | Num | OUTPUT.

B — A DECLARE needs a colon between the identifier and its data type: DECLARE Name : STRING. Every DECLAREd variable then gets its own trace table column.

D — Count does not change when it is output, so its cell should be left blank: ' | 1'. Only write a value in a cell when that variable changes.