将选择的文字从大写字母转换为小写字母（反之亦然）；

Convert a selection of text from uppercase to lowercase (or vice versa).

youdao

返回一个字符串，该字符串中的所有字母都被转换为小写字母。

Returns a string where all alphabetic characters have been converted to lowercase.

youdao

这个例程检查字符是否在A到Z之间，然后将其转换为小写字母并将它直接和其他字符比较。

This routine checks to see if a character is between a and Z, then converts it to lowercase and compares it; it compares other characters directly.

youdao

It's passing to this function called toupper, which if you've never used it it actually does what it says it makes it touppercase.

它把这个传递给toupper函数，如果你们使用过，它表示的是把小写字母,转换为大写字母。

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