如何迭代目標c中的NSString？

Question

如何遍歷目標c中的NSString對象，並維持當前所處字符的索引？

我想將每三個字符的ASCII值增加3，然後在用戶界面的標籤中打印這個增加的字符。

Answer 1

不清楚您是否只是打印遞增的字符或全部。如果前者，你會怎麼做：

NSString *myString = @"myString"; 
NSMutableString *newString = [NSMutableString string]; 
for (int i = 0; i < [myString length]; i++) 
{ 
    int ascii = [myString characterAtIndex:i]; 
    if (i % 3 == 0) 
    { 
     ascii++; 
     [newString appendFormat:@"%c",ascii]; 
    } 
} 
myLabel.text = newString; 

Answer 2

這會做詭計嗎？

NSString *incrementString(NSString *input) 
{ 
    const char *inputUTF8 = [input UTF8String]; // notice we get the buffers so that we don't have to deal with the overhead of making many message calls. 
    char *outputUTF8 = calloc(input.length + 1, sizeof(*outputUTF8)); 

    for (int i = 0; i < input.length; i++) 
    { 
     outputUTF8[i] = i % 3 == 0 ? inputUTF8[i] + 3 : inputUTF8[i]; 
    } 

    NSString *ret = [NSString stringWithUTF8String:outputUTF8]; 
    free(outputUTF8); // remember to free the buffer when done! 
    return ret; 
}