1 NSString *s1 = @"0123456789";

1                NSString *s4 = @"abcdefg";2         NSString *s4_sub = [s4 substringToIndex:3];3         NSLog(@"subStr:%@, %d", s4_sub, @"abc" == s4_sub); // abc, 04         NSLog(@"subStr:%@, %d", s4_sub, [@"abc"isEqualToString:s4_sub]); // abc, 1

1         NSLog(@"The character at index 2 --> %c",[s1 characterAtIndex:2]); // 22         NSRange range = [s1 rangeOfString:@"234"];3         if (range.location != NSNotFound) {4                 NSLog(@"%@", NSStringFromRange([s1 rangeOfString:@"234"])); // {2, 3}5         }

1         NSString *s3 = [NSStringstringWithFormat:@"%@%@", s1, s2];2         NSLog(@"%@", [@"www."stringByAppendingString:@"baidu.com"]); // www.baidu.com

1 （1）- (NSArray) componentsSeparatedByString:(NSString *)

1         NSLog(@"%@", [@"aBc"uppercaseString]); // ABC2         NSLog(@"%@", [@"AbC"lowercaseString]); // abc

1         NSLog(@"extension : %@", [@“test.txt" pathExtension]); // txt

1         NSLog(@"%ld", [@"0123456789"length]); // 10

1         NSLog(@"%@", [s1 substringWithRange:NSMakeRange(2, 3)]); // 包含index, 2342         NSLog(@"%@", [s1 substringFromIndex:2]); // 包含index, 234567893         NSLog(@"%@", [s1 substringToIndex:2]); // 不包含index, 01

1         if (s1 == nil || s1.length == 0) {2             NSLog(@"字符串为空");3         }

1         NSLog(@"%d", [@"0123456789"hasPrefix:@"012"]); // 12         NSLog(@"%d", [@"0123456789"hasSuffix:@"789"]); // 1

 1         // 基本数据类型 int float double char 2         3         // 1.int类型转换成字符串 4         int a = 10; 5         NSString *s1 = [NSStringstringWithFormat:@"%d", a]; 6         NSLog(@"s1 is %@", s1); 7         8         // 2.float -> NSString 9         float f = 3.1415f;10         NSString *s2 = [NSStringstringWithFormat:@"%.4f", f];11         NSLog(@"s2 is %@", s2);12        13         // 3.double -> NSString14         double d = 3.1415;15         NSString *s3 = [NSStringstringWithFormat:@"%.4f", d];16         NSLog(@"s3 is %@", s3);17        18         // 4.char -> NSString19         char c = ‘A‘;20         NSString *s4 = [NSStringstringWithFormat:@"%c", c];21         NSLog(@"s4 is %@", s4);22        23         // 5.NSString -> int24         NSString *s5 = @"433";25         int a2 = [s5 integerValue];26         NSLog(@"a2 = %d", a2);27        28         // 6.NSString -> float29         NSString *s6 = @"3.1415";30         float f2 = [s6 floatValue];31         NSLog(@"f2 = %.4f", f2);32        33         // 7.NSString -> double34         NSString *s7 = @"3.1415";35         double d2 = [s7 doubleValue];36         NSLog(@"d2 = %.4f", d2);37        38         //注意, 传入的字符串必须是符合格式要求的, 才能返回正确结果39         NSLog(@"i123 double format = %f", [@"i123"doubleValue]); // 0.00000040        41         // 8.NSString -> char42         NSString *s8 = @"a";43         char c2 = [s8 characterAtIndex:0];44         NSLog(@"c2 = %c", c2);