Totalling, Counting & String Handling

🎯 Syllabus & Goals 3 min

Cambridge 8.1.4 · Totalling and counting 8.1.4 · String handling Paper 2 · Algorithms, Programming and Logic

By the end of this lesson you can:

1. Write totalling and counting statements inside a loop, in pseudocode and Python.
2. Use LENGTH, SUBSTRING, UCASE and LCASE — and the Python equivalents — on a string.
3. Explain why pseudocode strings start at position 1 but Python strings start at index 0.

Textbook: Chapter 8, §8.1.4(d)–(e) (pp. 314–317)

Recap / Warm-Up 5 min

Last lesson: three loops — FOR … NEXT, WHILE … DO … ENDWHILE and REPEAT … UNTIL. Loops are where totalling and counting happen.

Quick starter

Before a loop adds numbers into Total, what value must Total be given — and why?

🧠 Key Concept 14 min

1 · Totalling and counting

Total ← Total + Weight
Count ← Count + 1

total = total + weight
count = count + 1
count += 1          # Python shorthand, same effect

2 · String handling

A string is a sequence of characters, from an empty string ("") up to a maximum set by the language. Each character has a position number. You must know four string operations:

Worked Example 12 min

Example 1 · Totalling and two kinds of counting

A parcel depot inputs parcel weights until -1 is entered. Output the number of parcels, their total weight and how many weigh more than 10 kg. Test data: 4.5, 12, 7.5, -1.

1. Initialise the total and both counters to 0 before the loop.they must start from nothing.
2. Input the first weight before a WHILE loop, and the next one at the end of the body.the -1 is tested before it can be added or counted.
3. Every parcel is counted; only heavy parcels are counted inside an IF.a conditional count.

CONSTANT Heavy ← 10
DECLARE Weight, TotalWeight : REAL
DECLARE ParcelCount, HeavyCount : INTEGER
TotalWeight ← 0
ParcelCount ← 0
HeavyCount ← 0
OUTPUT "Parcel weight in kg (-1 to stop): "
INPUT Weight
WHILE Weight <> -1 DO
  TotalWeight ← TotalWeight + Weight
  ParcelCount ← ParcelCount + 1
  IF Weight > Heavy
    THEN
      HeavyCount ← HeavyCount + 1
  ENDIF
  OUTPUT "Parcel weight in kg (-1 to stop): "
  INPUT Weight
ENDWHILE
OUTPUT "Parcels: ", ParcelCount
OUTPUT "Total weight: ", TotalWeight, " kg"
OUTPUT "Heavy parcels: ", HeavyCount

# Parcel depot: total weight, number of parcels, number of heavy parcels
HEAVY = 10
total_weight = 0
parcel_count = 0
heavy_count = 0
weight = float(input("Parcel weight in kg (-1 to stop): "))
while weight != -1:
    total_weight = total_weight + weight     # totalling
    parcel_count = parcel_count + 1          # counting every parcel
    if weight > HEAVY:
        heavy_count += 1                     # counting only some
    weight = float(input("Parcel weight in kg (-1 to stop): "))
print("Parcels:", parcel_count)
print("Total weight:", total_weight, "kg")
print("Heavy parcels:", heavy_count)

Parcel weight in kg (-1 to stop): 4.5
Parcel weight in kg (-1 to stop): 12
Parcel weight in kg (-1 to stop): 7.5
Parcel weight in kg (-1 to stop): -1
Parcels: 3
Total weight: 24.0 kg
Heavy parcels: 1

Example 2 · String handling — usernames and letter counts

(a) A school makes a username from the first three letters of a student's first name and family name, in capitals.

DECLARE FirstName, FamilyName, UserName : STRING
OUTPUT "First name: "
INPUT FirstName
OUTPUT "Family name: "
INPUT FamilyName
UserName ← SUBSTRING(FirstName, 1, 3) & SUBSTRING(FamilyName, 1, 3)
UserName ← UCASE(UserName)
OUTPUT "Your username is ", UserName
OUTPUT "It has ", LENGTH(UserName), " characters"

# Make a username from the first 3 letters of each name
first_name = input("First name: ")
family_name = input("Family name: ")
username = first_name[0:3] + family_name[0:3]
username = username.upper()
print("Your username is", username)
print("It has", len(username), "characters")

First name: Alex
Family name: Morgan
Your username is ALEMOR
It has 6 characters

1. SUBSTRING("Alex", 1, 3) → "Ale"; SUBSTRING("Morgan", 1, 3) → "Mor".start at position 1 and take 3 characters.
2. & joins them: "AleMor".& is concatenation in pseudocode; Python uses + on strings.
3. UCASE gives "ALEMOR", and LENGTH is 6.the result is assigned back, so UserName really changes.

(b) Count how many times the letter "a" appears in a sentence, ignoring capitals. This combines a loop, LCASE, SUBSTRING and counting.

DECLARE Sentence : STRING
DECLARE Position, CountA : INTEGER
OUTPUT "Enter a sentence: "
INPUT Sentence
Sentence ← LCASE(Sentence)
CountA ← 0
FOR Position ← 1 TO LENGTH(Sentence)
  IF SUBSTRING(Sentence, Position, 1) = "a"
    THEN
      CountA ← CountA + 1
  ENDIF
NEXT Position
OUTPUT "The letter a appears ", CountA, " times"

# Count how many times the letter a appears in a sentence
sentence = input("Enter a sentence: ")
sentence = sentence.lower()          # so "A" and "a" both count
count_a = 0
for position in range(0, len(sentence)):
    if sentence[position] == "a":
        count_a = count_a + 1
print("The letter a appears", count_a, "times")

Enter a sentence: A banana
The letter a appears 4 times

Notice the loop ranges: pseudocode goes from 1 TO LENGTH(Sentence); Python goes from 0 up to (not including) len(sentence). Both visit every character exactly once.

Try It Yourself 12 min

📝 Exam Practice 10 min

🗝️ Recap & Key Terms 3 min

Initialise, then add: totalling adds the value, counting adds one. For strings, learn LENGTH, SUBSTRING(s, start, length), UCASE and LCASE — and remember pseudocode starts at position 1, Python at index 0.

Totalling

Keeping a total that values are added to.

Counting

Keeping track of the number of times an action is performed.

Length

The number of characters in a string, including spaces.

Substring

Part of a string, extracted from a start position for a given number of characters.

Upper / lower

Converting all the letters in a string to upper case / lower case.

Concatenation

Joining two strings end to end (& in pseudocode, + in Python).

Homework 1 min

Task (≤ 15 min): Write pseudocode that inputs 10 words using a FOR loop and outputs how many of them are longer than 6 characters, and the total number of characters in all 10 words. [5]

DECLARE Word : STRING
DECLARE Index, LongCount, TotalChars : INTEGER
LongCount ← 0
TotalChars ← 0
FOR Index ← 1 TO 10
  OUTPUT "Enter a word: "
  INPUT Word
  TotalChars ← TotalChars + LENGTH(Word)
  IF LENGTH(Word) > 6
    THEN
      LongCount ← LongCount + 1
  ENDIF
NEXT Index
OUTPUT "Words longer than 6 letters: ", LongCount
OUTPUT "Total characters: ", TotalChars