0
Still curious? Ask our experts.
Chat with our AI personalities
Beau
Fran
Jordanundefined means a variable has been declared but has not yet been assigned a value. On the other hand, null is an assignment value. It can be assigned to a variable as a representation of no value. Also, undefined and nullare two distinct types: undefined is a type itself (undefined) while null is an object
Add your answer:
Earn +20 pts
What is the difference between null pointer ASCII null character and null string?
A null pointer is a pointer which does not point to any valid memory location, and usually contains the binary value "0" to represent this (this is language dependent). The ASCII null character is a character-sized zero value (in ASCII, it is an unsigned byte with a value of 0), and typically represents the end of a string (esp. as in C and C++). A null string is one that is zero characters of usable string data; in a length-based string, this means the length parameter is set to 0, and in an ASCII null-terminated string, means the first character is set to 0.
If null is compared with null what is the result-true or false or null or unknown?
You mean SQL? NULL = anything IS NULL NULL <> anything IS NULL ... NULL IS NULL = TRUE NULL IS NOT NULL = FALSE
What is the difference between an array shift and unsetting a variable in PHP?
By shifting the values in an array, you are moving a key's value to the previous key. The very first key's value is obliterated. By shifting all values in the array, all keys will have a value of NULL. Unsetting a variable is entirely different -- performing a variable unsetting causes the variable to have a value of NULL, as if it was never set.
What is the difference between a null pointer and a null macro?
Using a NULL macro to make C portableI'll assume that you're asking your question for C type language programming. A NULL pointer is a pointer that's guarnteed to point to nothing. This may be 0 in a UNIX/Linux system or some other address in another system. Using the NULL macro to set/initialize your pointers will make your programs more portable among systems than using something like the 0.#include char *c = 0; // initialize to NULL--not portablechar *p = NULL; // initialize to NULL as defined in stdio is portableAddendumThe code:char *c = 0;actually is portable because the compiler converts 0's used in a pointer context (cast to a pointer) to the machine's representation of a NULL pointer, which may or may not be all 0 bits. The NULL macro itself might be defined as something like 0 or (void *)0, and both definitions are portable. As a corollary, the following code is also portable:if (!c) {// do something}because it is equivalent to:if (c != 0) {// do something}and the 0 above is converted to a NULL pointer because it is being compared with a pointer.
C plus plus program of periodic table?
The Periodic Table Of Elements has a well defined order. The layout can be emulated easily since the arrangement is quite logical.The first step would be to define a struct containing the following members as a minimum:- atomic number (int - number of protons in its nucleus)- symbol (char* - short form of the element name)- name (char* - long form of the element name)i.e.:struct elementinfo {int atomicnumber;char *symbol, *name;};Other members can be added as your program develops.The next step is to arrange the table itself. If you're using Win32 or another graphical system, it's a matter of drawing a box (Win32 would require a MoveToEx() call and four LineTo() calls) and TextOut() (or a related function) for the atomic number and element symbol (centered horizontally and aligned top and bottom respectively).Including conio.h or curses.h would give you the ability to position the cursor and even change the text color, allowing for an alternate "graphical" method.To keep things simple, storing the elements in an array would require something akin to the following:struct elementinfo elementlist[]={{1, "H", "Helium"}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {2, "He", "Helium"},{-1, NULL, NULL},{3, "Li", "Lithium"}, {4, "Be", "Beryllium"}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{0, NULL, NULL}, {0, NULL, NULL}, {0, NULL, NULL},{5, "B", "Boron"}, {6, "C", "Carbon"}, {7, "N", "Nitrogen"},{8, "O", "Oxygen"}, {9, "F", "Fluorine"}, {10, "Ne", "Neon"},{-1, NULL, NULL},...{-2, NULL, NULL}};In the above array, {0, NULL, NULL} represents a blank displayed for that particular cell, and {-1, NULL, NULL} represents a newline. The {-2, NULL, NULL} signifies the end of the table. The following for() loop would wrap around your display code like so:for (count=0; elementlist[count].atomicnumber!=-2; count++) {if elementlist[count].atomicnumber==-1) {// jump to next line of elements}else {// display current element}}Drawing this graphically, you'd have to keep track of the current cursor (X, Y) position.If you are sending this to stdout or another text stream (i.e. text file), you could draw each line, referencing the array of elements as you go. The list of elements would have to be stored in a nested array: the outermost array contains each line of elements in an array. This would do away with the {-1, NULL, NULL} terminating each line of elements.Extending this code to use classes would be relatively simple, but might only make sense if you were drawing this graphically storing each element as an object.The Lanthanides and Actinides, since they're displayed separately from the main table, would probably have to be stored separately for sake of convenience.Also, as laboratories continue to synthesize (or, on the rare chance, discover) new elements, the layout of the table may change (even drastically) to suit. Thus, the code would have to be altered accordingly.See the related links below for more ideas on how to design a program that displays the Periodic Table of Elements.(Note: Code originally posted was copyrighted. Added to related links.)
