|) operator instead of Logical AND(&&) operator [closed]

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This is what I code for program which do case conversion of string :

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我很困惑，为什么我不能使用逻辑OR(||)运算符，而不是逻辑AND(&&)运算符，在行 if(str[i]>='a'&& str[i]<='z')

Answer 1

There are other possible characters after 'z' and below 'a' (ascii table), so it's necessary to do both upper and lower bounds checks with &&. If you used the || operator then the statement could execute if the character were any value, because ALL characters are greater than 'a' or less than 'z'.