objective-c - 替换字符串中的字符

Question

我有一个 NSMutableString @"hello"。我想将第二个位置的字符“e”替换为“a”，以便它读取 @"hallo"。我该怎么做？

我尝试使用此方法来实现 Shift Cipher，但它抛出 IndexOutBoundsException

- (NSString*)encode:(NSString*)original withShift:(int)shift {

    NSMutableString* encoded = [NSMutableString stringWithString:original];
    for (int i=0; i < [encoded length]; i++) {
        char oriChar = [encoded characterAtIndex:i];
        if (oriChar == ' ') {
            continue;
        }
        char encChar = ((oriChar - LETTER_POS) + shift) % ALPHABET_LENGTH + LETTER_POS;

        NSRange range = {i, i};
        [encoded replaceCharactersInRange:range withString:[NSString stringWithUTF8String:&encChar]];

    }
    return encoded;

}

Answer 1

NSRange r = {1,1}; //String indexing is 0-based
[s replaceCharactersInRange: r withString:@"a"]

此外，请务必学习使用在线引用。