//将NSData转化为NSString
        NSString* str = [[NSString alloc] initWithData:response encoding:NSUTF8StringEncoding];
//将NSString 转化为NSData 
(NSString.h)
- (NSData *)dataUsingEncoding:(NSStringEncoding)encoding;

//载一个字符串中删除一个字符或字符串
[_display deleteCharactersInRange:NSMakeRange(index_of_char_to_remove, 1)];

数学转换为字符串
NSString *returnStr;
returnStr = [[NSNumber numberWithInt:row] stringValue];

NSString  
    *******************************************************************************************/  
    //一、NSString      
      
      
    //1、创建常量字符串。  
    NSString *astring = @"This is a String!";  
      
    //2、创建空字符串，给予赋值。  
      
    NSString *astring = [[NSString alloc] init];  
    astring = @"This is a String!";  
    [astring release];  
    NSLog(@"astring:%@",astring);  
   
    //3、在以上方法中，提升速度:initWithString方法  
      
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];  
    NSLog(@"astring:%@",astring);  
    [astring release];  
      
    //4、用标准c创建字符串:initWithCString方法  
      
    char *Cstring = "This is a String!";  
    NSString *astring = [[NSString alloc] initWithCString:Cstring];  
    NSLog(@"astring:%@",astring);  
    [astring release];  
      
    //5、创建格式化字符串:占位符（由一个%加一个字符组成）  
      
    int i = 1;  
    int j = 2;  
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"%d.This is %i string!",i,j]];  
    NSLog(@"astring:%@",astring);  
    [astring release];  
      
    //6、创建临时字符串  
      
    NSString *astring;  
    astring = [NSString stringWithCString:"This is a temporary string"];  
    NSLog(@"astring:%@",astring);  
      
          
      
    NSString *path = @"astring.text";  
    NSString *astring = [[NSString alloc] initWithContentsOfFile:path];  
    NSLog(@"astring:%@",astring);  
    [astring release];  
          
    NSString *astring = [[NSString alloc] initWithString:@"This is a String!"];  
    NSLog(@"astring:%@",astring);  
    NSString *path = @"astring.text";      
    [astring writeToFile: path atomically: YES];  
    [astring release];      
      
              
      
    //用C比较:strcmp函数  
      
    char string1[] = "string!";  
    char string2[] = "string!";  
    if(strcmp(string1, string2) = = 0)  
    {  
        NSLog(@"1");  
    }  
      
    //isEqualToString方法      
    NSString *astring01 = @"This is a String!";  
    NSString *astring02 = @"This is a String!";  
    BOOL result = [astring01 isEqualToString:astring02];  
    NSLog(@"result:%d",result);

//compare方法(comparer返回的三种值)      
    NSString *astring01 = @"This is a String!";  
    NSString *astring02 = @"This is a String!";      
    BOOL result = [astring01 compare:astring02] = = NSOrderedSame;      
    NSLog(@"result:%d",result);      
    //NSOrderedSame判断两者内容是否相同

NSString *astring01 = @"This is a String!";  
    NSString *astring02 = @"this is a String!";  
    BOOL result = [astring01 compare:astring02] = = NSOrderedAscending;      
    NSLog(@"result:%d",result);  
    //NSOrderedAscending判断两对象值的大小(按字母顺序进行比较，astring02大于astring01为真)

NSString *astring01 = @"this is a String!";  
    NSString *astring02 = @"This is a String!";  
    BOOL result = [astring01 compare:astring02] = = NSOrderedDescending;      
    NSLog(@"result:%d",result);       
    //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)

//不考虑大小写比较字符串1  
    NSString *astring01 = @"this is a String!";  
    NSString *astring02 = @"This is a String!";  
    BOOL result = [astring01 caseInsensitiveCompare:astring02] = = NSOrderedSame;      
    NSLog(@"result:%d",result);       
    //NSOrderedDescending判断两对象值的大小(按字母顺序进行比较，astring02小于astring01为真)

//不考虑大小写比较字符串2  
    NSString *astring01 = @"this is a String!";  
    NSString *astring02 = @"This is a String!";  
    BOOL result = [astring01 compare:astring02  
                            options:NSCaseInsensitiveSearch | NSNumericSearch] = = NSOrderedSame;      
    NSLog(@"result:%d",result);       
      
    //NSCaseInsensitiveSearch:不区分大小写比较 NSLiteralSearch:进行完全比较，区分大小写 NSNumericSearch:比较字符串的字符个数，而不是字符值。  
      
      
          
      
    NSString *string1 = @"A String";   
    NSString *string2 = @"String";   
    NSLog(@"string1:%@",[string1 uppercaseString]);//大写  
    NSLog(@"string2:%@",[string2 lowercaseString]);//小写  
    NSLog(@"string2:%@",[string2 capitalizedString]);//首字母大小  
      
      
              
      
    NSString *string1 = @"This is a string";  
    NSString *string2 = @"string";  
    NSRange range = [string1 rangeOfString:string2];  
    int location = range.location;  
    int leight = range.length;  
    NSString *astring = [[NSString alloc] initWithString:[NSString stringWithFormat:@"Location:%i,Leight:%i",location,leight]];  
    NSLog(@"astring:%@",astring);  
    [astring release];  
      
      
              
      
    //-substringToIndex: 从字符串的开头一直截取到指定的位置，但不包括该位置的字符  
    NSString *string1 = @"This is a string";  
    NSString *string2 = [string1 substringToIndex:3];  
    NSLog(@"string2:%@",string2);

//-substringFromIndex: 以指定位置开始（包括指定位置的字符），并包括之后的全部字符  
    NSString *string1 = @"This is a string";  
    NSString *string2 = [string1 substringFromIndex:3];  
    NSLog(@"string2:%@",string2);

//-substringWithRange: //按照所给出的位置，长度，任意地从字符串中截取子串  
    NSString *string1 = @"This is a string";  
    NSString *string2 = [string1 substringWithRange:NSMakeRange(0, 4)];  
    NSLog(@"string2:%@",string2);  
      
      
    //扩展路径  
      
    NSString *Path = @"~/NSData.txt";  
    NSString *absolutePath = [Path stringByExpandingTildeInPath];  
    NSLog(@"absolutePath:%@",absolutePath);  
    NSLog(@"Path:%@",[absolutePath stringByAbbreviatingWithTildeInPath]);

//文件扩展名  
    NSString *Path = @"~/NSData.txt";  
    NSLog(@"Extension:%@",[Path pathExtension]);