截取：
NSString *str1 = @"this is zero";
1.从第三个字符开始，截取长度为2的字符串.........注:空格算作一个字符
NSString *str2 = [str1 substringWithRange:NSMakeRange(5,2)];//str2 = "is"
2.截取从0位到第n为（第n位不算在内）
NSString *str3 = [str1 substringToIndex:4];//str3 = "this"
3.从第n为开始直到最后（包含第n位）
NSString *str4 = [str1 substringFromIndex:8];//str4 = "zero"
4.截取字符串的后4位
NSString *str5 = [str1 substringFromIndex:str1.length - 4];//str5 = "zero"
5.去掉字符串的后4位
NSString *str6 = [str1 substringToIndex:str1.length - 4];//str6 = "this is "
6. 去掉字符串的头4位
NSString *str7 = [str1 substringWithRange:NSMakeRange(4,str1.length - 4)];//str7 = " is zero"
匹配
NSString *string =@"sd是sfsfsAdfsdf";
NSRange range = [string rangeOfString:@"Ad"];//匹配得到的下标
NSLog(@"rang:%@",NSStringFromRange(range)); rang:{8, 2}
string = [string substringWithRange:range];//截取范围内的字符串
NSLog(@"截取的值为：%@",string);截取的值为：Ad
分隔
NSString *string =@"sdfsfsfsAdfsdf";
NSArray *array = [string componentsSeparatedByString:@"A"]; //从字符A中分隔成2个元素的数组
NSLog(@"array:%@",array); //结果是adfsfsfs和dfsdf
数组与字符串的转化（有分隔符）
将string字符串转换为array数组
NSArray *array = [str componentsSeparatedByString:@","];--分隔符
将array数组转换为string字符串
NSString *str = [array componentsJoinedByString:@","];--分隔符
拼接
NSString *str1 = @"kkk";
NSString *str2 = @"ggg";
NSString *strpingjie = [NSString stringWithFormat:@"@%@%",str1,str2];
