iOS学习——第二天练习题

1.构建一个字符串（This is a string!）,并打印出来 stringWithFormat stringWithString
2.判断字符串长度，并打印出来 length
取出字符串第3个位置的字符，并打印 characterAtIndex
3.构建2个字符串，把连个字符串拼接起来，并打印 stringByAppendingString
4.定义一个长度为20的字符串，取出前10个字符，并打印 substringToIndex
去掉前10个字符，并打印 substringFromIndex
5.把字符串全部改成大写，并打印 uppercaseString
全部改为小写，并打印 lowercaseString
6.构建2个字符串，比较大小，并打印结果 isEqualToString/compare
7.构建一个数值型的字符串，转化成int、bool、float、double类型 intValue boolValue floatValue doubleValue

8.构建字符串"My story is the type of twists and turns or ups and downs of melodrama“将这句话的单词拆分，并保存到NSArray数组里面，打印该数组 componentsSeparatedByString
#import"AppDelegate.h"

@implementation AppDelegate

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary
*)launchOptions
{
// Override point for customization after application launch.
NSString *str=@"This is a string!";
NSString *str1=[NSStringstringWithFormat:@"%@",@"This
is a string!"];

NSString *str2=[NSString
stringWithString:str];
NSLog(@"str1 = %@ str2 = %@",str1,str2);

NSInteger len=str1.length;//[str1
length];

NSLog(@"len:%d",len);

char c;
c=[str1characterAtIndex:3];

NSLog(@"%c",c);

NSString *str3=@"hello";

NSString *str4=@"world";

NSString *str5=[str3 stringByAppendingString:str4];

NSLog(@"%@",str5);

NSString *str6=@"0123456789abcdefghij";

NSString *str7=[str6 substringToIndex:10];

NSString *str8=[str6 substringFromIndex:10];

NSLog(@"前十 %@后十 %@",str7,str8);

NSString *str9=@"HelloWorld";

NSString *str10=[str9 uppercaseString];

NSString *str11=[str9 lowercaseString];

NSLog(@"大写 %@小写 %@",str10,str11);

if([str3 isEqualToString:str4])
{

NSLog(@"两个字符串相等");
}

else
{

NSLog(@"两个字符串不相等");
}

NSInteger i=[str3 compare:str4];

if(i==0)
{

NSLog(@"equal");
}

else if(i==1)
{
NSLog(@"first bigger");
}

else
{
NSLog(@"second bigger");
}

NSString *str12=@"123.12";

NSLog(@"int %d",[str12
intValue]);

NSLog(@"bool %d",[str12
boolValue]);

NSLog(@"float %.2f",[str12
floatValue]);

NSLog(@"double %.2f",[str12
doubleValue]);//保留小数点后两位

NSString *str13=@"My story is the type of twists and turns or ups and downs
of amelodrama";
NSArray *s;
s=[str13 componentsSeparatedByString:@" "];//@"
"里面为空格，空格为分隔符

NSLog(@"%@",s);

returnYES;
}

输出结果：