知识点指南

Strings

String problems treat text as a sequence of characters or words. The code usually scans characters, counts matches, compares neighbours, or builds a new string.

什么时候使用

读题时可以留意这些信号。

The input contains words, letters, symbols, or encoded commands.
The task asks about patterns, repeated letters, initials, or transformations.
Character-by-character processing matches the story rule.

常见错误

提交前可以检查这些小陷阱。

Forgetting that strings are indexed like arrays.
Building a huge string when only a length or count is needed.
Ignoring exact case or exact symbol requirements.

怎么写成代码

把知识点翻译成变量、循环、判断和更新。

Read strings with normal string variables.
Access characters by index when position matters.
Use a loop over characters when every symbol is checked the same way.
Build output with append/+= only when the actual constructed string is required.

在 Block 题里长什么样

答题时通常会看到这些步骤被拆成代码块。

1Read the string or list of strings.
2Initialise count/result.
3Loop over characters or words.
4Check the target character/pattern.
5Update count or append to result.
6Print the final count/result.

题目里怎么出现

读题时先找这些信号，再决定答案区应该选哪些 blocks。

The statement says string, word, character, letter, binary, code, or initials.
The output is a count of symbols or a new string.
Exact matching matters, including uppercase/lowercase.

Count a target character

一个小型模板，展示代码和 blocks 的对应关系。

C++

int count = 0;
for (char c : S) {
    if (c == target) {
        count++;
    }
}
cout << count << '\n';

Python

count = 0
for c in S:
    if c == target:
        count += 1
print(count)

对应 block 顺序

1Read the string.
2Initialise count to 0.
3Loop through each character.
4Check whether the character is the target.
5Increase count.
6Output count.