Strings and string handling

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Notes de leçon Diapos Questions d'entraînement

Notes de leçon

What a string is

A string is a sequence of characters (letters, digits, symbols). Strings are written in quotation marks: "Hello".

Zero-based string positions

Common operations

Length: LEN("Hello") = 5.
Concatenation: joining strings: "Hello" + " " + "World" = "Hello World".
Substrings: part of a string by position (usually starting at 0): "Computer".SUBSTRING(0,3) = "Com".
Case: UPPER and LOWER convert the case.
Position/indexing: the first character is at index 0.
Searching: finding where a character or word appears; checking if a string contains a substring.
ASCII conversion: ASC("A") = 65 and CHR(65) = "A".

String length and case

Comparing strings

For the simple ASCII examples here, comparison is case-sensitive and follows character codes: apple comes before banana and A differs from a.
Language-specific collation and Unicode processing can differ; state comparison and normalisation rules when needed.

Common tasks

Reverse a non-empty string by visiting indices LEN(s) − 1 down to 0 and appending each character to an initially empty result.
A palindrome equals its reverse under the chosen comparison rules. Check for an empty string before accessing s[0]; counting vowels can use traversal and selection.

Casting and conversion

Convert numbers to strings and back when joining or calculating.

ASCII conversion

ASC gives a character code
CHR gives the character
ASC("A") = 65

Characters and ASCII codes

Diapos

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Questions d'entraînement

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1.What is a string?
Easy
- Aa sequence of characters
- Ba whole number
- CTrue or False
- Da decimal
2.What is concatenation?
Easy
- Ajoining strings together
- Bsplitting strings
- Cdeleting strings
- Dsorting strings
3.Using the zero-based indexing convention in this lesson, what is the first character’s index?
Easy
- A0
- B1
- C-1
- D2
4.What does UPPER("abc") return?
Easy
- A"ABC"
- Bthe number 3
- C"CBA"
- Dan error
5.What does LEN do?
Easy
- Areturns the number of characters
- Breturns the first character
- Cjoins strings
- Ddeletes characters
6.Using zero-based start and a length argument, what is "Hello".SUBSTRING(1,3)?
Easy
- A"ell"
- B"Hel"
- C"llo"
- D"Hello"
7.What is LEN("Hello World")?
Easy
- A11
- B10
- C12
- D2
8.What is "Good" + " " + "Day"?
Easy
- A"Good Day"
- B"GoodDay"
- C"Good Day"
- D"Day Good"

Plus de questions

9.What is ASC("A")?
Easy
- A65
- B97
- C1
- D0
10.What is CHR(66)?
Easy
- A"B"
- B"A"
- C"C"
11.What is the 3rd character of "Cat" (index 2)?
Easy
- A"t"
- B"C"
- C"a"
- D"at"
12.Using case-sensitive ASCII-code comparison, which statement is true?
Medium
- A"apple" < "banana"
- B"banana" < "apple"
- C"apple" = "Apple"
- D"z" < "a"
13.What does ASC("a") - ASC("A") equal?
Medium
- A32
- B1
- C0
- D26
14.How would you check if a word is a palindrome?
Medium
- Acompare it with its reverse
- Bcount its letters
- Cconvert to uppercase only
- Dfind its length
15.Here STRING converts a number to text and + joins strings. What is output? word = "cat"; OUTPUT UPPER(word) + STRING(LEN(word))
Medium
- ACAT3
- BCAT
- C3CAT
16.What is the output? s = "abc" OUTPUT s[0] + s[2]
Medium
- Aac
- Bab
- Cbc
- Dabc
17.What does LOWER("PYTHON") give?
Medium
- A"python"
- Bthe number 6
- C"nohtyp"
- Dan error
18.Which code reverses a string s?
Medium
- Aloop from the last index to 0 adding each character
- Bloop from 0 to the last index
- Cuse MOD
- Duse DIV
19.What does ASC(CHR(70)) return?
Medium
- A70
- B71
- C"F"
- D0
20.If + concatenates strings, what does "5" + "3" produce?
Medium
- A"53"
- B8
- C"8"
- Dan error
21.Which is an example of data validation using strings?
Medium
- Achecking an email contains an @ symbol
- Badding two numbers
- Csorting numbers
- Ddrawing a flowchart
22.What does 'substring' mean?
Easy
- Aa contiguous character sequence taken from a string
- Ba data type that can contain only integers
- Ca Boolean operator
- Dthe number of bytes in every file
23.What does 'upper case' mean?
Easy
- Acapital letters
- Bsmall letters
- Cnumbers
- Dsymbols
24.Which index is the last character of "Code" (length 4)?
Medium
- A3
- B4
- C5
- D0
25.Why can case matter in a case-sensitive ASCII string comparison?
Medium
- A"A" and "a" have different codes
- Bit does not matter
- Cthey are equal
- Dstrings have no case
26.A string is a sequence of characters.
Easy
True or false?
27.Concatenation joins strings.
Easy
True or false?
28.In the zero-based convention used here, string indices start at 1.
Easy
True or false?
29.A palindrome reads the same forwards and backwards.
Easy
True or false?
30.LEN("Computer") returns 7.
Medium
True or false?
31.Which are string operations?
Medium
- Alength
- Bconcatenation
- Csubstring
- Dchanging case
- Ecompiling
32.Which words are palindromes?
Medium
- Alevel
- Bradar
- Cnoon
- Dkayak
- Ecomputer
33.Write pseudocode to input a string, output its length, and output its first character if it is non-empty; otherwise output "No first character".
Medium

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