First character at position zero or one

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Date:

Class:

Quick Questions

Shade in the A or B circle for each question.

1. In Cambridge pseudocode, what does SUBSTRING("Computer", 1, 1) return?

A "C" (position 1 is the first character)

B "o" (position 1 is the second character)

2. Which statement matches the syllabus examples for SUBSTRING?

A The first character of a string is at position 1

B The first character of a string is at position 0

3. Counting from 1, what does SUBSTRING("Python", 2, 3) return?

A "yth"

B "tho"

4. A language counts positions from 0. What does the same call, SUBSTRING("Python", 2, 3), return there?

A "yth"

B "tho"

5. Which call gets the first letter of Word in Cambridge pseudocode?

A SUBSTRING(Word, 0, 1)

B SUBSTRING(Word, 1, 1)

Match the Pairs

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

Left column		Right column
1SUBSTRING(Word, 1, 1)		ASUBSTRING(Word, 1, 3)
2Word[0]		BReturns the first character of Word, because Cambridge pseudocode numbers the first character as position 1
3With one-based numbering, the first three letters of Word start at position 1		CStarting at 0 is wrong in Cambridge pseudocode, where the first character is position 1. The start should be 1.
4The same call returns different characters under each numbering rule. With Word ← "CAT", this call gives "C" if counting from 1 but "A" if counting from 0		DGets the first character in a language that counts positions from 0, such as Python
5FirstLetter ← SUBSTRING(Name, 0, 1)		EThe answer does not state whether positions start at 0 or 1, so the result is ambiguous. State the numbering used in an exam answer.
6// Takes the 2nd letter: SUBSTRING(Word, 2, 1) with no numbering stated		FSUBSTRING(Word, 2, 1)

Definitions

SUBSTRING(Word, 1, 1)

Fill in the Blanks

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

First ← SUBSTRING(Word, _, 1)

Word ← "CODE" OUTPUT _________(Word, 1, 2)

Word ← "CODE" Second ← SUBSTRING(Word, _, 1)

Word ← "CODE" Last ← SUBSTRING(Word, _, 1)

// Python counts from _, Cambridge from 1

Spot the Error

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

Question 1

A DECLARE Word : STRING

B DECLARE First : CHAR

C Word ← "Cambridge"

D First ← SUBSTRING(Word, 0, 1)

E OUTPUT First

Question 2

A Word ← "Python"

B Letter ← SUBSTRING(Word, 2, 1)

C OUTPUT Letter

D // outputs P

Question 3

A Name ← "Zoe"

B Initial ← SUBSTRING(1, Name, 1)

C OUTPUT Initial

Question 4

A // 0 is the first character

B Word ← "Hello"

C Second ← SUBSTRING(Word, 2, 1)

D OUTPUT Second

Question 5

A Word ← "Dog"

B Last ← SUBSTRING(Word, 2, 1)

C OUTPUT Last

D // outputs g

Answer Key

First character at position zero or one

Section A: Quick Questions

A — "C" (position 1 is the first character)

A — The first character of a string is at position 1

A — "yth"

B — "tho"

B — SUBSTRING(Word, 1, 1)

Section B: Match the Pairs

SUBSTRING(Word, 1, 1) → Returns the first character of Word, because Cambridge pseudocode numbers the first character as position 1

Word[0] → Gets the first character in a language that counts positions from 0, such as Python

With one-based numbering, the first three letters of Word start at position 1 → SUBSTRING(Word, 1, 3)

The same call returns different characters under each numbering rule. With Word ← "CAT", this call gives "C" if counting from 1 but "A" if counting from 0 → SUBSTRING(Word, 2, 1)

FirstLetter ← SUBSTRING(Name, 0, 1) → Starting at 0 is wrong in Cambridge pseudocode, where the first character is position 1. The start should be 1.

// Takes the 2nd letter: SUBSTRING(Word, 2, 1) with no numbering stated → The answer does not state whether positions start at 0 or 1, so the result is ambiguous. State the numbering used in an exam answer.

Section C: Definitions

SUBSTRING(Word, 1, 1) — Position 1 is the first character in Cambridge pseudocode, so this returns the first letter. Some languages count from 0 instead, so state which numbering you use.

Section D: Fill in the Blanks

First ← SUBSTRING(Word, 1, 1)

Word ← "CODE"
OUTPUT SUBSTRING(Word, 1, 2)

Word ← "CODE"
Second ← SUBSTRING(Word, 2, 1)

Word ← "CODE"
Last ← SUBSTRING(Word, 4, 1)

// Python counts from 0, Cambridge from 1

Section E: Spot the Error

D — Cambridge pseudocode numbers the first character as position 1, so position 0 does not exist. The start position should be 1 to get the first letter.

B — Position 2 is the second character, so this would output y, not P. To get the first letter the start position must be 1.

B — The arguments are in the wrong order. SUBSTRING takes the string first, then the start position (1 for the first character), then the length.

A — The comment states the wrong numbering. In Cambridge pseudocode the first character is position 1, which is why position 2 gives the second letter, e.

B — Counting from 0, position 2 would be the last letter, but Cambridge pseudocode counts from 1. Dog has 3 characters, so the last one is at position 3. Position 2 gives o.