Labels are identifiers followed by a colon, i. They are implementation details that functions hide from one another. They are local variables declared in a block. The identifiers can be reused elsewhere without ambiguity.
There are such kind of problems that the direct solution can not be easily expressed, but the relationship between the problem and its simpler version is explicit. Thus the problem can be simplified repeatedly reduced to a smaller version, until it reaches the simplest case called "base case", and finally becomes known. In short, recursion keeps producing simpler version of the original problem until the base case is revealed.
From logical point of view, recursion is invalid or impractical: you can not use an unknown solution to solve a problem. Therefore it is simple. Iteration solutions are better than recursion in respect to performance, because recursion produces a series of function calls and copies of variables, thus takes more overhead, which iteration can avoid. Recursion is only good when it can mirror the real-world problem more naturally, thus the program is easier to understand and debug.
This is called "exponent explosion". Try to avoid this situation. If the result of the calculation depends on the order of evaluation of the two operands i.
A constant variable or pointer should be initialized when declared. In most cases it is achieved by using of qualifier "const". It is also used to define a local variable that shouldn't be changed. Any attempt to modify the constant variable will be checked out by compiler before the program is run. Using this principle to properly design software can greatly reduce debugging time and improper side effects, and can make a program easier to modify and maintain.
Compared with the function call overhead, the program size reduced by not repeatedly include the block of statements may be trivial. In these cases we put "inline" qualifier in front of the function definition to tell compiler to insert the body of the called function into the calling function to avoid a call.
When the inline function is changed, all functions that call it should be re-compiled. Keyword inline is specially useful for wrapper classes. The copy constructor of the passed object is called to make the copy, requiring extra overhead. The original values are untouched. This is good for data security, but bad for performance.
A reference is not a variable. It is just an alias of a variable. When we talk about a variable, it is actually the address of one memory cell used to hold different values.
In machine language we would directly use the address to represent the variable, but in high-level languages identifiers are used to present addresses. Although "b" is created "out of" a, but once created they are equal. Therefore, when a object is passed by reference, a new alias is created in the called function to refer to the address of that object. With this alias the called object can do anything directly to the object itself. The calling statement of call-byreference is the same as call-by-value, therefore the programmer may forget that he is calling by reference.
When the values of the parameters are the default ones, you can omit the parameters. It is a system-dependent keystroke combination. This calculation has the same priority as manipulation and division. For example, the result of int with float is float.
So do not compare floating-point values for equality. Instead, test whether the absolute value of the difference is less than a specified small value. Using assignment operator can save a bit of compiling and running time. It is useful when the statement is in a loop which will be run many times. As a complete loop, first the condition is checked, if satisfied, the statement is executed, then the control variable is incremented. Notice that break can only exit one layer of loop. If the number of initializers are less than the number of the array elements, the remaining elements are automatically initialized to zero.
But such kind of expression can only be used in declaration. In such way when you need the change the array size you only need to change one place. Only constant variable can be used as array size. Therefore you can not make the array size dynamic by inputting an integer from keyboard in run time and use it as array size. Therefore by declaring an array of 3 elements then putting a value into the 4th element, you may have overwritten another variables and produced very serious logic errors which is very difficult to find out.
Therefore, the size of an array should be carefully observed. An array such as char buf[80] however, points to a block of memory allocated by the compiler. If a block of characters ends with NULL i. Because the bytes are constant, you can never amend the content of the string. Therefore, if you want to amend the content of "Hello world! You have to copy the constant bytes into a character array: char str[]; strcpy str, "Hello world! You can then amend the content of the array later. Because as said before, the array name is a constant pointer which can not be assigned.
So it is not a NULL-terminated string and can not be used in string manipulation functions such as strcpy, strlen, strcat, etc. Average comparison time: half of the array size. Binary search: can only be applied on sorted array. By checking the middle element you will find out which half of the array contains the element. Maximum comparison time: log n arraysize.
If an array needs to be searched frequently, then it is worthwhile to spend a great time to sort it first. The first dimension does not need a number, just like single-dimension arrays, but the subsequent dimensions does. An n x 3 array is located in the memory in such a sequence: 0, 0 0, 1 0, 2 1, 0 1, 1 1, If the compiler knows the number of columns which is 3, it will put the fist element 0, 0 of first row on the first memory location, the first element on second row on the fourth memory location, the first element on third row on the 7th location, Without the number of columns the compiler is not able to organize memory for the array.
A pointer with a value of 0 points to nowhere. If a pointer is a constant pointer, it should be initialized when declared, and it can not be pointed to any other variable. Because of this, a pointer can be used in the called function to receive the array.
Then by moving the pointer e. If the size of the variable to which the pointer is pointing to is 4, then actually the value of the pointer will be increased by 3 x 4. Any type of pointer can be assigned to a pointer to void without casting. However, it can not be conversed. The result may show which one is pointer to a highernumbered element. Pointer arithmetic including increment and difference is meaningless unless performed on one array, because we are only sure that array elements are located one after another.
We can not assume two separate variables are put together in the memory. The following four expressions is doing the same thing: cout cout cout cout 5. When a pointer is pointed to an array or a string, it is actually pointed to the first element of the array subscription 0.
This element can also be represented by ptr[3]. If you point a pointer to the middle of an array, what will happen?
The pointer can be used as the name of a new array, whose first element is the element to which the pointer is pointing to. Notice that the number of bytes for a certain type is different for different systems.
Just like an array name is the address of the first array element, a function name is a actually the starting address of the function code. A function pointer holds the address of a function, just like a float pointer holds the address of a float variable. A function pointer can point to either a global function or a class function. My name is Jessy! My name is John! When you want your program to be applicable to different use cases, you may find that at a certian point in your program, you need to invoke a function which has the same signature but different implementation for different use cases.
Different client who uses your program may have different implementations. In this case, you have to provide a mechanism so that the client may register his own version of that function to your program before the invoking point, so that your program knows which one to call. There are three ways to achieve call-back. The OO approach of callback is to let the client class inherit from and implement an interface.
In your code you simply hold an interface pointer and call the interface methods through that pointer. The client program will create his implementation object, assign its pointer to the interface pointer in your class before the calling pointer in your class is reached.
However, if the client class is already finished and did not implement the interface you want, you have to use a less OO approach.
The client programmer or your do it for him should write a separate matching class for the client class, which inherit from the desired interface with the function you will call back, which provides the service you need by manipulating client-class objects. In your code you have a pointer to the interface and invoke the service provided by the separate class. The least OO approach is to use function pointers like the above example. The user is prompted to select an option from a menu e. Each option is severed by a different function.
Pointers to different functions is stored in an array of function pointers. It is extremely flexible and therefore can generate every kind of errors if misused. For example, you can only cast an object of a sub-class to its super-class. No other casting between user-defined classes is allowed.
However, pointers to different classes can be cast to each other without any restrict. What is passed in the casting is only the address. So you can cast a pointer to an integer to a Employee-class pointer.
Then the Employee pointer will just assume that starting from the passed address it can find all attributes of Employee class. From now on we will talk more about OO issues. As a class, it combined the data attributes and the behavior attributes of an object together, and formed an object which can simulate both aspects of a real-world object.
To distinguish independent functions such as those string handling functions in "string. The "public:" and "private:" labels are called "member access specifiers".
All data members and methods declared by the "public" specifier are accessible from outside, and all declared by "private" are only accessible for methods. Actually an object contains only the data members. Methods do not belong to any specific object. The belong to the class. All objects share one copy of methods. It may improve the performance, but it is not good for information hiding, because the client of the object is able to "see" the implementation of its methods.
Almost all the workplaces use computers to perform computer related work and it also does the work faster if used wisely. Generally, we all are familiarize with the some basic operations of computer like opening, shutting down, surfing net and other but it is not enough to perform technical work. There are many books and study materials available to learn some advanced computer skills like typing, Microsoft office, data mining etc. Computer fundamentals by p.
We do insist that you abide by the rules and policies detailed below. If you agree to the terms, please check the 'I agree' checkbox and press the 'Complete Registration' button below. If you would like to cancel the registration, click here to return to the forums index. Although the administrators and moderators of FaaDoOEngineers. All messages express the views of the author, and neither the owners of FaaDoOEngineers. By agreeing to these rules, you warrant that you will not post any messages that are obscene, vulgar, sexually-oriented, hateful, threatening, or otherwise violative of any laws.
The owners of FaaDoOEngineers. For the aspirants who are preparing for competitive exams CCC course certification is important. In various exams it is mandatory to have a CCC course certification to apply and to appear in the exam.
So, the candidate who are preparing or wants to prepare for competitive exams, then one should also prepare for CCC exam and apply and qualify the CCC exam to become eligible for various exams. After complete reading of the ccc book with practice, one can easily qualify the doeacc ccc examination.
0コメント