C/C++ :: Difference Between Literal And Symbolic Constants?
Jun 29, 2014
"A constant, like a variable, is a memory location where a value can be stored. Unlike variables, constants never change in value. You must initialize a constant when it is created. C++ has two types of constants: literal and symbolic.
A literal constant is a value typed directly into your program wherever it is needed. For example, consider the following statement:
long width = 5
This statement assigns the integer variable width the value 5. The 5 in the statement is a literal constant. You can't assign a value to 5, and its value can't be changed.
The values true and false, which are stored in bool variables, also are literal constants.
A symbolic constant is a constant represented by a name, just like a variable. The const keyword precedes the type, name, and initialization. Here's a statement that sets the point reward for killing a zombie:
const int KILL_BONUS = 5000;
Whenever a zombie is dispatched, the player's score is increased by the reward:
playerScore = playerScore + KILL_BONUS;
If you decide later to increase the reward to 10,000 points, you can change the constant KILL_BONUS and it will be reflected throughout the program. If you were to use the literal constant 5000 instead, it would be more difficult to find all the places it is used and change the value. This reduces the potential for error."
what's the difference? Here is a program to demonstrate what I'm having trouble conceptualizing.
#include <iostream>
using namespace std;
int main() {
int width = 10, length = 10;
int area = width * length;
cout << "Width: " << width << endl;
cout << "Length: " << length << endl;
cout << "Area: " << area << endl;
return 0;
}
Now, why would it be harder to go in and changed a regularly defined integer than one defined with the 'const' keyword proceeding it? For example, the width and length variables. My confusion comes from the point that they seem to both simply be variables with a value assigned to them. I feel as if the process of having to change a literal constant's value is synonymous to the process of having to change a symbolic constant's.
My assignment is to create a simple stock broker program that ask the user how much they are willing to invest and ask what company they would like to invest in. Finally it outputs how many shares the user will have based on their investment amount. My code is below. My professor said to declare symbolic constants and factor out the if else statements. Ive been struggling trying to understand constant variables. How do I use const variables to factor out the if else statements?
****************************************************************** CSCI 240 Program 5 Part 2 Spring 2013
Programmer: Section: 1 Date Due: 3/1/13
Purpose: This program uses functions to calculate the surface area of various shapes. It is an exercise in learning to write functions. ******************************************************************/
#include <iostream> #include <iomanip> using namespace std; #define PI 3.14 //Symbolic constant for the value of PI
int Menu(); int getValue( string prompt, int lowerBound, int upperBound );
I am working on a code that is suppose to get vowels and consnants from a string. So far i got up to trying to get the vowels from a string. this is what i have so far:
#include <iostream> #include <string> // includes go into header using namespace std; int getword(string word); int getvowels(string word);
I need to write a program in which you do the following:
Define three named constants using the appropriate data types: DEC_NUM = 65; HEX_NUM = 0x7a; LETTER = 'f';
Then display each of these constants in decimal, in hexadecimal, and as a character using cout. Your program will have a total of nine cout statements.
why strcmp() doesn't return true when comparing a string constant with a string that was acquired via a linked list. By the way, the data in the linked list was taken from a text file. Does that imply that there's a new line () character in the string from the linked list?
I'm incrementing the pointer to buffer 150 bytes beyond its reserved 50. I see testwalk, followed by bracketout, followed by bracketin printed by the overflow on buffer.
The memory locations are ordered descending from their call order. Why is this the case?
One would think that they would be written in ascending order as I call them. I can only assume that they're compiled bottom up - where could I read about this process?
I have a binary identifier which I tried to make a constexpr since all of its calculations would never occur during runtime (this is true for literal identifiers, right?). Since constant expressions can only have one instruction, I tried to cheat a little and returned an immediate call to a lambda function. This failed miserably however. I tried making a constexpr function pointer and called that from _binary down below, but the compiler still felt that it wasn't a constexpr. Why is this? And is there a way to make a function like _b below constexpr?
#include <iostream> #include <cstddef> using std::cout; using std::endl; long unsigned //Original operator"" _b(const char* const literal, size_t lsize){
In C++ there are a number of primitives that are not defined in terms of other types. By this I'm thinking
int a = 1; char b = 'M'; float c = 3.45f; short d = 0xC3A3;
Is it possible to define your own literal? What I would like to do is have a hex literal for a data type where n = sizeof(data_type). If this type were a big integer, then I would want something like:
BigInt e = 0x13CA9B0C98D983E912DA0B0A9F87E0;
My goal is to assign a value from one contingous chunk of bytes and to not do it with a string.
In another forum, this example code fragment was stated as being an example of undefined behavior. My understanding is that a literal string exists from program start to program termination, so I don't see the issue, even though the literal string is probably in a different part of memory.
Code: /* ... */ const char *pstr = "example"; /* or even */ char *pstr = "example"; /* as long as no attempt is made to modify the data pointed to by pstr, */ /* unless pstr is later changed to point to a stack or heap based string */
these function works. but if i concat literal strings with '+', i must use '(string)'. so i'm trying overload the operator + for concat literal strings, but without sucess:(
In the following char array, notice the use of a backspace character in a string literal: ''.
char text1[50] = "aHello, World! Mistakee was "Extra 'e'"! ";
What exactly does a backspace character do here? When the compiler evaluates this line, does it actually delete the previous character, like when you press the backspace button on the keyboard?
how string literal that works with the cin object?
char * str = "This is a string constant";
Is the str stored the address of the first character of the string literal?
But some books just state that the pointer-to-char (char pointer) stores the address of the string literal". So just wonder how it is.
When it is used with cout, cout just treats it like a string and instead of printing the address, it just prints out all characters one by one until it reaches the terminated null character.
If this is the case, then I am just wondering how cin works with it? with a statement like this cin >> str; ?
Does the computer allocate enough memory for it? and then cin stores the first character into the first address and then advances to the next address and stores the next character?
The problem with that is that string.data isn't considered const during the initialization of the String struct so the compiler throws an error. It doesn't feel very elegant to do it like this either way.
Is there an elegant solution to this problem? I would like to avoid making a copy of the string literal.
What shall I learn in order to send values from 0.00 to 5.00? I'm working with they Hitachi 16x2 LCD display.I've been sending/displaying literal values on it all day.
Code:
SendCharater(unsigned char val)
where the variable val corresponds to the LCD character table.I can also send Hello World to the display, like so:
Code:
void putsXLCD(unsigned char *buffer){ while(*buffer) // Write data to LCD up to null { while( BusyXLCD() ); // Wait while LCD is busy SendCharacter(*buffer); // Write character to LCD buffer++; // Increment buffer } return; }
I could type in putsXLCD("5.00") in order to display it on the LCD, but how do I implement this automatically for values, e.g. 0.00 to 5.00?It appears I can only pass literal values through the function SendCharacter, meaning that in order to display "0" I have to pass the value 0x30 (the hex value of "0" on the LCD Table).
My current thought process:Much like passing "Hello World" in the function putsXLCD(), I need to assign a pointer that points at each value in the "array" that I need to send. E.g., I need to send 3.24, so I need to point to "3", fetch the corresponding hex value in the LCD table, in this case 0x34, and the pass this 0x34 into the SendCharacter function, and so on. So, if this is the case, how can I fetch the corresponding hex value?
I'm making a .json loader for a project that I'm working on, and to simplify things, I decided to make all the root attributes named in a separate file. Here's my problem: my loading function, Add(const char* id), works just fine when I pass it a string literal.
However, when I use a function that iterates through a vector list, even with the exact same definitions as the literal, it returns the error: std::out_of_range at memory location 0x0026fb30
I've stepped through it with the VS2010 debugger about a hundred times, checked against memory locations, and just have done everything I can think of, all to no avail..
Background: I'm using SDL and CodeBlocks and trying to make a Graphics class that would simplify some SDL operations such as drawing and loading images.
Issue: The loadImage function in the graphics class fails to load the image correctly and so the program prints out a blank window during run-time. I've tried multiple ways of passing a string literal into the function the surface temp fails to load and so background in Game fails to load. After testing it several times, I'm pretty sure that the issue lies with SDL_LoadBMP not registering the passed variable for whatever reason. I know the image is in the right place as writing SDL_LoadBMP("./Graphics/image.bmp"); brings it up just fine.
Current Code:
Main simply creates a Game object and execute(), so I didn't feel the need to put it on here.
Output: A blank window. (It should show the background image but doesn't.)
Note: I originally wrote it as gfx.loadImage(background, "./Graphics/image.bmp") but that gives me a conversion warning and still fails to show the image when the program runs. I've tried looking up examples similar to what I was doing but no one else seems to have this problem.
Very new to programming, and I know that there must be another way on inputting a string into each array cells not by just inputting it one by one, but as a whole. My code at the meantime is: [URL]
