NSString* startSubstring = [originalString substringToIndex:5]; // "This "

NSString* endSubstring = [originalString substringFromIndex:5]; // "is An EXAMPLE"

// make a range
NSRange theRange = NSMakeRange(2,5); // note： NSRange is not an Objective-C class, but rather a plain old C structure.

NSString* substring = [originalString substringWithRange:theRange]; // "is is" 

if ([firstString isEqualToString:secondString]) { 
    // Do something
}

// note: isEqualToString is case-sensitive

SString* sourceString = @"Four score and seven years ago";
NSRange range = [sourceString rangeOfString:@"SEVEN"
                     options:NSCaseInsensitiveSearch];

// create
NSArray* myArray = @[@"one", @"two", @"three"];

NSArray* myArray = @[@"one", @"two", @"three"];
int index = [myArray indexOfObject:@"two"]; // should be equal to 1

if (index == NSNotFound) {
    NSLog(@"Couldn't find the object!");
}

NSArray* myArray = @[@"one", @"two", @"three"];
for (NSString* string in myArray) {
    // this code is repeated 3 times, one for each item in the array
}

NSMutableArray* myArray = [NSMutableArray arrayWithArray:@[@"One", @"Two"]]; 

// Add "Three" to the end
[myArray addObject:@"Three"];
// Add "Zero" to the start
[myArray insertObject:@"Zero" atIndex:0];
// The array now contains "Zero", "One", "Two", "Three".
[myArray removeObject:@"One"]; // removes "One"
[myArray removeObjectAtIndex:1]; // removes "Three", the second
                                 // item in the array at this point
// The array now contains just "Two"

// replace
[myArray replaceObjectAtIndex:1 withObject:@"Bananas"];
myArray[0] = @"Null";

NSDictionary* translationDictionary = @{
    @"greeting": @"Hello",
    @"farewell": @"Goodbye"
};

NSDictionary* translationDictionary = @{@"greeting": @"Hello"};
NSString* greeting = translationDictionary[@"greeting"];

// foreach

// Here, aDictionary is an NSDictionary
for (NSString* key in aDictionary) { 
    NSObject* theValue = aDictionary[key];
}

NSMutableDictionary* aDictionary = @{};
aDictionary[@"greeting"] = @"Hello";
aDictionary[@"farewell"] = @"Goodbye";

NSNumber* theNumber = @123;
int myValue = [theNumber intValue];
// 'numbers' is an NSMutableArray
[numbers addObject:theNumber];

int a=100;
NSNumber* number = @(a+1);

// Assuming that there is a text file at /Examples/Test.txt:
NSString* filePath = @"/Examples/Test.txt";
NSData* loadedData = [NSData dataWithContentsOfFile:filePath];

// Here, loadedData is an NSData object
NSString* filePath = @"/Examples/Test.txt";
[loadedData writeToFile:filePath atomically:YES];