第一：基本数据类型与字符串转换

//基本数据类型(int float,double char)

1）基本数据类型—>NSString       //1.int类型换换成字符串int a = 88;NSString * str1 = [NSString stringWithFormat:@"%d",a];       //2.float -> NSStringfloat f = 0.8;NSString * str3 = [NSString stringWithFormat:@"%.1f",f];//3.double - >NSstring double d = 66.2222; NSString * str4 = [NSString stringWithFormat:@"%.4f",d];       //4.char - > NSStringchar c = ‘b';NSString * str5 = [NSString stringWithFormat:@"%c",c];       2）NSString-—>基本数据类型     //5.NSString -> int NSString * str6 = @"1";int i1 = [str6 intValue];       //5.NSString -> floatNSString * str7 = @“8.8";float f1 = [str7 floatValue];       //6.NSString -> doubleNSString * str8 = @"8.88";double d1 = [str8 doubleValue];       //注意:当你要把字符串转换成某种基本数据类型的时候,一定要确定你要转化你的数据是正确NSString * str9 = @“a123";int i2 = [str9 intValue];       //7.将字符串中的字母转换成大写 NSString * str10 = @“apple";NSString * tmpStr1 = [str10 uppercaseString];NSLog(@"tmpStr1 %@ str10 %@",tmpStr1,str10);       //8.将字符中的字母转换成小写NSString * str11 = @“APPLE";NSString * tmpStr2 = [str11 lowercaseString];//9.将首字母大写NSString * str12 = @“apple";NSString * tmpStr3 = [str12 capitalizedString];

第二：字符串重组

//1.多个数据拼接成一个字符串int year = 1990;int month = 8;int day = 08;NSString * date = [NSString stringWithFormat:@"%d年%d月%d日",year,month,day];NSString * address = @“上海";NSString * dateAndAddrss = [NSString stringWithFormat:@"%@地址:%@",date,address];//2.字符串的末尾追加新的字符NSString * str1 = @"apple.";NSString * str2 = [str1 stringByAppendingString:@"iphone"];//3.在指定的范围追加字符串NSString * str3 = @"apple";NSRange range = {4,0};//location代表的时从哪个索引开始插入,length 代表的意思可以覆盖几个字符NSString * str4 = [str3 stringByReplacingCharactersInRange:range withString:@"iphone"];//4.使用新的字符,替换原有的字符NSString * str5 = @“apple,iPhone";NSString * str6 = [str5 stringByReplacingOccurrencesOfString:@“p" withString:@“q"];//5.在字符串中删除特定的某些字符 胡汉三 hhsNSString * str7 = @“apple-iphone—.iwatch.itouch";NSString * str8 = [str7 stringByReplacingOccurrencesOfString:@"-" withString:@""];//6.去掉字符串中的空格NSString * str9 = @“apple iPhone iwatch";NSString * str10 = [str9 stringByReplacingOccurrencesOfString:@" " withString:@""];

第三： 字符串写入文件

3.1:将字符串写入到文件NSString * content = @"今天马路上捡到一分钱";NSString * path = @"/Users/tengfei/Desktop/test.txt";//1.NSString *:要给入文件目录(并且要包括文件名称)//2.atomically : YES//3.NSUTF8StringEncoding 国际通用的编码格式//4.NSError 是用来记录错误信息的NSError * error;//writeToFile:<#(NSString *)#> atomically:<#(BOOL)#> encoding:<#(NSStringEncoding)#> error:<#(NSError *__autoreleasing *)#>BOOL result = [content writeToFile:path atomically:YES encoding:NSUTF8StringEncoding error:&error];if(result){    NSLog(@"文件创建成功");}else{    NSLog(@"error %@",error);}  3.2：从文件中读取字符串内容  //要给出文件路径  //你写入文件的时候,使用的是什么编码格式,读取的时候就要用什么编码格式NSString * path = @"/Users/tengfei/Desktop/test.txt";NSError * error;NSString * str = [NSString stringWithContentsOfFile:path encoding:NSUTF8StringEncoding error:&error];if (error != nil){    NSLog(@"error message %@",error);}else{    NSLog(@"str content %@",str);}

第四：可变字符串

//1.创建可变字符串//NSMutableString 继承自 NSString//NSMutableString 拥有NSString所有的属性以及方法//NSMutableString * muStr = [[NSMutableString alloc] init];NSMutableString * muStr = [[NSMutableString alloc] initWithCapacity:0];//是初始化字符串内容[muStr setString:@"apple"];//动态的给字符串末尾追加新值[muStr appendString:@".com"];//在指定的索引位置,插入字符串[muStr insertString:@“iphone" atIndex:3];//删除指定范围的字符串//你要删除的长度,一定不能够超出字符串的的长度,导致异常Range or index out of boundsNSRange range = {3,7};// [muStr deleteCharactersInRange:range];[muStr replaceCharactersInRange:range withString:@"苹果"];