// C String to NSString
const *char cString = "Hello";
NSString *myNSString = [NSString stringWithUTF8String:cString];

const *char cString = "Hello";
NSString *myNSString = [NSString stringWithCString:cString encoding:NSASCIIStringEncoding];

// NSString to C String
NSString *str = @"123";
const char *cStr = str.UTF8String;