Strings
Introduced| English | Meaning |
|---|---|
| string/strɪŋ/ | A sequence of characters treated as a single data value. |
| ordered sequence/ˈɔːdəd ˈsiːkwəns/ | ordered sequence |
| characters/ˈkærɪktəz/ | A text unit such as a letter, digit, punctuation mark or other symbol. |
| Concatenation/kənˌkætəˈneɪʃn/ | Joining sequences, such as strings, end to end. |
| Length/leŋθ/ | The distance between two points. |
| substring/ˈsʌbstrɪŋ/ | A part of a string: from "computer" you can take "put". |
| user input/ˈjuːzə ˈɪnpʊt/ | user input |
Text is a string
- Text in a program is stored as a string 字符串.
- A string is an ordered sequence 有序序列 of characters 字符.
- "Hello" is a string of five characters.
- Order matters, so "abc" and "cba" are different strings.
A string is:
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Order matters, so "abc" ≠ "cba".
Concatenating "sun" and "flower" gives:
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Concatenation joins them in order into one string.
What is the length of the string "cat"?
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It has 3 characters: c, a, t.
String operations
- Concatenation 拼接 joins strings into one: "sun" + "flower" gives "sunflower".
- Length 长度 is how many characters a string holds — the length of "cat" is 3.
- A substring 子串 is a part of a string: from "computer" you can take "put".
- You can also read one character by its position.
Characters are numbered from 1; concatenation joins strings end to end
Index and slice a string
Every character has a position (index from 0). A slice takes characters from the start index up to — but not including — the end index.
If counting starts at 0, the character at position 0 of "cat" is:
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Position 0 is the first character, "c".
A part of a string, such as "put" from "computer", is called a ______.
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A substring is a slice of the original string.
Positions and indexing
- Positions are counted from a starting number.
- Many languages start at $0$, so in "cat" position $0$ is "c" and position $2$ is "t".
- A substring takes characters from a start index up to — but not including — an end index.
- Always check where a language starts counting.
Concatenating "Hi, " + "Ana" + "!" produces:
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The three strings join in order to greet the user.
Processing user input
- These operations process user input 用户输入 — text a user types, like a name.
- A program might read a name, find its length, and greet the user by joining strings.
Greeting. Read the name "Ana" into name; its length is 3. Build the greeting by concatenation: "Hi, " + name + "!" gives "Hi, Ana!" — the output shown to the user.
A string is an ordered sequence of characters, so order matters. Key operations are concatenation (join), length (count), and substring (a part). Positions are usually indexed from 0, and a slice runs up to but not including the end index. Strings let a program process user input.