//1.int类型换换成字符串        int a = 10;        NSString * str1 = [NSString stringWithFormat:@"%d",a];        NSLog(@"str1 %@",str1);                //2.float -> NSString        float f = 2.4;        NSString * str3 = [NSString stringWithFormat:@"%.1f",f];        NSLog(@"str3 %@",str3);                //3.double - >NSstring        double d = 65.9898;        NSString * str4 = [NSString stringWithFormat:@"%.4f",d];        NSLog(@"str4 %@",str4);                //4.char - > NSString        char c = ‘c‘;        NSString * str5 = [NSString stringWithFormat:@"%c",c];        NSLog(@"str5 %@",str5);                //5.NSString -> int        NSString * str6 = @"1";        int i1 = [str6 intValue];        NSLog(@"i1 %d",i1);                //5.NSString -> float        NSString * str7 = @"9.8";        float f1 = [str7 floatValue];        NSLog(@"f1 %.1f",f1);                //6.NSString -> double        NSString * str8 = @"8.88";        double d1 = [str8 doubleValue];        NSLog(@"d1 %.2f",d1);                //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 = @"i386";        int i2 = [str9 intValue];        NSLog(@"is %d",i2);                //7.将字符串中的字母转换成大写        NSString * str10 = @"china";        NSString * tmpStr1 = [str10 uppercaseString];        NSLog(@"tmpStr1 %@ str10 %@",tmpStr1,str10);                //8.将字符中的字母转换成小写        NSString * str11 = @"CHINA";        NSString * tmpStr2 = [str11 lowercaseString];        NSLog(@"tmpStr2 %@",tmpStr2);                //9.将首字母大写        NSString * str12 = @"china";        NSString * tmpStr3 = [str12 capitalizedString];        NSLog(@"tmpStr3  %@",tmpStr3);