IOS中怎样把一个字符串倒序输出

    NSString * str = @"abcdefg";

    NSMutableString * string = [[NSMutableString alloc]initWithCapacity:str.length];

    int j = (int)str.length;

    for (int i = j - 1; i >= 0; i--) {

        [string appendFormat:@"%c", [str characterAtIndex:i]];

    }

    NSLog(@"string____%@",string);