Variables in C++ - Reading Assignment

[Dan_O_Kane]

1. A variable is a named object representing representing memory locations. Meaning you’ve got yourself a higher level language.
   My ex c++ programmer boss in a java role used to complain constantly about not being able to override the behaviour of the native types in java. I’m glad that was the case.
2. A variable is a named region of memory
3. Instantiation is a declaration statement called a definition in code which the compiler uses to interpret the code we write using that variable.
4. An l-value is stored in an object addressed memory location for use later in the program whereas an r-value is calculated, used and discarded.
5. An uninitialized variable is a declared variable which has not been instantiated. It can create unexpected results.
6. Undefined behaviour results from execution of code whose behavior is not well defined by the language.

[Ouzo69]

1. What is a variable in C++?
A variable is a name given to a memory location. It is the basic unit of storage in a program. The value stored in a variable can be changed during program execution. A variable is only a name given to a memory location, all the operations done on the variable effects that memory location.

2. What is the Definition of a variable?
A variable definition means that the programmer writes some instructions to tell the compiler to create the storage in a memory location. The syntax for defining variables is:

data_type variable_name;

or

data_type variable_name, variable_name, variable_name;

3. What is Instantiation of a variable?
A variable is initialized with a value. An object is instantiated when memory is allocated for it and it’s constructor has been run.

4. What is the difference between an l-value and an r-value?
First of all, let’s keep our heads away from any formal definition. In C++ an lvalue is something that points to a specific memory location. On the other hand, a rvalue is something that doesn’t point anywhere. In general, rvalues are temporary and short lived, while lvalues live a longer life since they exist as variables. It’s also fun to think of lvalues as containers and rvalues as things contained in the containers . Without a container, they would expire.

Let me show you some examples right away.

int x = 666;   // ok

Here 666 is an rvalue; a number (technically a literal constant ) has no specific memory address, except for some temporary register while the program is running. That number is assigned to x , which is a variable. A variable has a specific memory location, so its an lvalue. C++ states that an assignment requires an lvalue as its left operand: this is perfectly legal.

Then with x , which is an lvalue, you can do stuff like that:

int* y = &x;   // ok

Here I’m grabbing the the memory address of x and putting it into y , through the address-of operator & . It takes an lvalue argument and produces an rvalue. This is another perfectly legal operation: on the left side of the assignment we have an lvalue (a variable), on the right side an rvalue produced by the address-of operator.

However, I can’t do the following:

int y;
666 = y; // error!

Yeah, that’s obvious. But the technical reason is that 666 , being a literal constant — so an rvalue, doesn’t have a specific memory location. I am assigning y to nowhere.

This is what GCC tells me if I run the program above:

error: lvalue required as left operand of assignment

He is damn right; the left operand of an assigment always requires an lvalue, and in my program I’m using an rvalue ( 666 ).

I can’t do that either:

int* y = &666; // error!

5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?
An uninitialized variable is a variable that has not been given a value by the program (generally through initialization or assignment). Using the value stored in an uninitialized variable will result in undefined behavior, because you might get different values for this variable each time you run the program.

6. What is undefined behavior?
If your program’s behavior depends on the value of an uninitialized variable, you will never know what your program will be doing, because you might get a different value for this variable during the next execution of your program. Since you can’t figure out the value of an uninitialized variable during the next execution, you can’t determine the behavior of the program and therefore the behavior of this program is undefined.

[nwenzel0900]

1. What is a variable in C++?
   The name of an object.
2. What is the Definition of a variable?
   Declaring a statement with the name and type.
3. What is Instantiation of a variable?
   Execution from the cpu, that goes into memory.
4. What is the difference between an l-value and an r-value?
   I value is persistent in the memory and R value is not and are temporary.
5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?
   an unassigned variable that can be changed.
6. What is undefined behavior?
   Attempting to execute code that is not defined in the language.
   QUIZ
   1.Any information that can be moved,processed, or stored by a computer.
   2.A single piece of data stored in memory.
   3.A named object
   4.The name of an object
   5.Tells the computer what type of value the variable will store.
   6.A number that can be written without a fractional component.

[mickymax777]

1. A variable is a named object.
2. A special kind of declaration statement that is used to create a variable
3. “Instantiation of a variable” when it is assigned space in RAM
4. I-value is stored in memory, r-value can not be stored in memory.
5. “Uninitialized variable” has not been assigned a value – you can expect any value currently stored to its memory address.
6. “Undefined behaviour” is when the program exhibit unexpected results because the executing code is not well defined. “incorrect coding”

[MarcisB]

1. What is a variable in C++?

• Variable is a named object, a named piece of memory that contains a value.

2. What is the Definition of a variable?

• It is a statement where we state the type and name of the variable:
  int x;
  Statements in C++ are finished with ;

3. What is Instantiation of a variable?

• During instantiation, an object is created and a memory address is given to it.
• It is the execution of a Definition.

4. What is the difference between an l-value and an r-value?

• L-value is something that would go on the left side of a statement, like x.
• R-value is something that would go on the right side of a statement, like 42.
• This means that L-values have their place in memory. As mentioned, a variable is a place in memory with a name and L-value is that place/name.
• R-value is an object without a name. It is something used only once, like anonymous functions in Javascript.
• As I understand, if we type x = 42; 42 is R-value because we will only use it once to assign value to x. Then x is the L-value we will use further.

5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?

• If we type int x; a compiler takes some place in memory and calls it x. That place may already contain some random, unknown value and x will be that value until we define otherwise. Until then x is uninitiated.

6. What is undefined behavior?

• It is what happens when we execute code whose behavior is not fully defined by C++, like leaving uninitialized variables. In that case, the program might:
  – produce different result on every run;
  – produce right result once but wrong result on another run;
  – produce the same wrong result always;
  – crash;
  – work on some compilers but not on others;
  – work until we change some seemingly unrelated code.

[cryptomarls]

1. A variable is the name of an object.
2. The definition of a variable is a declaration that states the name and type of the variable.
3. Instantiation is when a variable is created and assigned a memory address.
4. I values have memory addresses, R values do not is just an expression
   5)It is a variable that hasnt been initialised a value. It would not compile properly resulting in odd behaviour.
5. it is when a variable is not initalised properly .

[LTL]

1. An object that has been named
2. A container where you can store data
3. Set a variable to store a specific data type
4. An l-value has an address in the memory, but an r-value does not
5. The variables data type will be set to what ever kind data is stored first
6. Program will throw an error if it detects unexpected results

[Rafael_Albuquerque]

1. What is a variable in C++?
   Named object in memory

2. What is the Definition of a variable?
   It’s to declare the variable’s name, value and data type

3. What is Instantiation of a variable?
   It’s the creation and placement in memory

4. What is the difference between an l-value and an r-value?
   An l-value is a value located in memory while r-value has no memory persistent location, as it’s discarded after execution.

5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?
   It’s a variable with no value assigned. In C++ it will assume the value that was already in the memory location assigned for the variable.

6. What is undefined behavior?
   The result of a code execution whose behavior is not well define by the language.

[Proniss]

1. a named object
2. a region of storage that has a value and other associated properties
3. the object will be created and assigned a memory address
4. l-values are values that have their place in memory, r-values are values (or expressions) that are discarded at the end of a statement and therefore need not to be associated with a memory address
5. A variable that has not been given a known value, it will hold the value of whatever was previously stored in that memory block
6. the result of executing code whose behavior is not well defined by the C++ language

[cryptomarls]

1. What is a variable in C++?
2. What is the Definition of a variable?
3. What is Instantiation of a variable?
4. What is the difference between an l-value and an r-value?
5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?
6. What is undefined behavior?

A1: A variable is a named object.
A2: It is a region of memory which holds the value and other properties.
A3: It is the creation of a variable. Before a variable can be used it must be assigned to a space in memory.
A4: The l-value references to the memory location of an object, (it is the identifier) it can be assigned on the left or right of the assignment operator(l-value = l-value). It can be of any type Int, float, etc…

The r-value references the actual data value that is stored at the memory address. It is an expression and can only be assigned on the right hand side of the assignment operator (= r-value)

A5: It is a variable that has not been assigned or initialised with a known value at the point of defining the variable. such a variable would result in unpredictable results.

A6: Undefined behaviour is the result of an uninitialised or badly defined variable.

[Marcus_Tang]

@ivan

• What is a variable in C++?
• What is the Definition of a variable?
• What is Instantiation of a variable?
• What is the difference between an l-value and an r-value?
• What is an uninitialized variable and what kind of behavior can you expect from such a variable?
• What is undefined behavior?

1)A variable is a named object.
2)A variable is a name which is associated with a value that can be changed
3)The object will be created and be assign with a memory address
4) An lvalue represents an object that occupies some identifiable location in memory and an rvalue is an expression that does not represent an object occupying some identifiable location in memory.
5)An uninitialized variable does not have any value as it hasn’t been assign with any memory by the compiler.
6)Undefined behavior occurs when a program does something the result of which is not specified by the standard.

[acey]

What is a variable in C++?

In C++ a variable is a named object. It is a region of storage that can store a data value.

What is Definition of a variable?

The definition of a variable is when it is allocated a name and a type by the compiler during compile time.

What is Instantiation of a variable?

The instantiation of a variable is when it gets created and assigned an address in memory during runtime.

What is the difference between an l-value and an r-value?

An l-value can have its address taken and be written to. An r-value cannot have its address taken and as such is read-only.

What is an uninitialized variable and what kind of behaviour can you expect from such a variable?

An unintialized variable is a variable that has been declared but not assigned a value. In C++ it will have a value of whatever garbage data that was in it’s memory location before. This may cause unpredictable behaviour and so it is good practise to initialise all variables with a default value before they are used.

What is undefined behaviour?

Undefined behaviour is the result of executing a program whose behaviour is prescribed to be unpredictable.

Article Quiz

1. What is data?

Data is a string of characters that represent information. Usually stored in binary format consisting of 0s and 1s.

2. What is a value?

A value is a unit of data that can be stored in a variable.

3. What is a variable?

A variable is a region of storage in memory that may be addressed using its identifier.

4. What is an identifier?

An identifier is a text value that a variable is named with to address it.

5. What is a type?

A type in C++ refers to the type of data a variable may be interpreted as.

6. What is an integer?

An integer type is used to store whole numbers without a decimal point or exponent.

[iplotnik]

1. A variable in C++ is a named region of memory.

2. The definition of a variable is a special kind of declaration statement.

3. Instantiation of a variable is the process of object creation and assigning it to a memory address.

4. l-value is a property of expression that points to a specific memory location. r-value is a property of expression that doesn’t point anywhere. r-values are temporary and short lived, while l-values live a longer life since they exist as variables.

5. A variable that has not been given a known value is called an uninitialized variable. An uninitialized variable may have your program crash and produce sporadic results.

6. Undefined behavior is the result of executing code whose behavior is not well defined by the C++ language.

[BTCBULLRDER]

1. What is a variable in C++?
   A variable is a named object.

2. What is definition of a variable?
   Variable definition is memory location for holding a value for objects.

3. What is instantiation of a variable?
   Instantiation means that object will be created & assigned a memory location.

4. What Is the difference between an I value and R value?
   I-value has persistent memory address
   R-value no persistent memory address

5. What is uninitialized variable & what kind of behavior can you expect from such a variable?
   Uninitialized variable is a variable that has not been given a known value (usually through initialization or assignment) & will be assigned a memory location by the compiler , the default value of that variable is whatever (garbage) value happens to already be in that memory location.

6. What is undefined behavior?
   Undefined behavior is the result of executing code whose behavior is not well defined by C++ language.

[Tordek]

1. What is a variable in C++?
   A named object.
2. What is Definition of a variable?
   A special kind of declaration statement.
3. What is Instantiation of a variable?
   It means the object will be created and assigned a memory address.
4. What is the difference between an l-value and an r-value?
   “l-value” refers to memory location which identifies an object. l-value may appear as either left hand or right hand side of an assignment operator(=). l-value often represents as identifier.
   R-value : r-value” refers to data value that is stored at some address in memory. A r-value is an expression that can’t have a value assigned to it which means r-value can appear on right but not on left hand side of an assignment operator(=).
5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
   A variable that has not been given a known value (usually through initialization or assignment). The default value of that variable is whatever (garbage) value happens to already be in that memory location!
6. What is undefined behaviour?
   It is the result of executing code whose behavior is not well defined by the C++ language.

[enrico]

1. What is a variable in C++? a region of memory with a name

2. What is the Definition of a variable? give a name (identifier) to the variable

3. What is Instantiation of a variable? creation of the variable associating a memory address

4. What is the difference between an l-value and an r-value? Ivalue have dedicated memory address, while rvalue don’t

5. What is an uninitialized variable and what kind of behavior can you expect from such a variable? a variable with no value assigned to it so the compiler will assign the value in its memory location (this could lead to errors because it could change every time)

6. What is undefined behavior? when execute code whose language is not defined, for example when execute code with uninitialized variable

[odesseus011]

1. What is a variable in C++?
   A variable is an object whereby objects are excluded.

2. What is the definition of a variable?
   When assigning a variable a value that will be acknowledged throughout the program.

3. What is instantiation of a variable?
   When an object is assigned a memory address.

4. What is the difference between an l-value and an r-value?
   An lvalue occupies a location in memory while rvalue does not.

5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
   When an object has not been given a known value yet. This could lead to unexpected results.

6. What is undefined behaviour?
   When a program is not defined for the required output. Basically anything can happen.

[letscrypto]

• What is a variable in C++?

A variable is a name for a value.

• What is the Definition of a variable?

The definition is the statement describing the variable’s name and type.

• What is Instantiation of a variable?

The instantiation is when the variable gets its first value.

• What is the difference between an l-value and an r-value?

And l-value is typically used in the left-hand side of an assignment, while an r-value is typically used on the right-hand side.

• What is an uninitialized variable and what kind of behavior can you expect from such a variable?

It is a variable that has not been initialized, and it counts as “undefined behavior”.

• What is undefined behavior?

Undefined behavior describes a situation in which there are no guarantees as to how the program will behave (it could behave very differently when run several times).

[MadAussie]

1. What is a variable in C++?
   Is a region of storage space that has a value with other associated properties.

2. What is the Definition of a variable?
   A named object is a variable. And the name of the object if the identifier.

3. What is Instantiation of a variable?
   Is when the compiler when runtime is operated a instance which assigns a variable a stored memory location. This is the Instantiation of a variable.

4. What is the difference between an l-value and an r-value?
   The L-value refers to a memory location which identifies an object.
   R-values is a temporary results of expressions, which don’t have an identifiable memory location.
   Another article I read referred too L-value;s a containers and R-values as things in the containers which I found useful understanding the differences a little more.

5. What is an uninitialized variable and what kind of behavior can you expect from such a variable?
   Is a variable when is declared before ti is defined. Usually a course of bugs in software.

6. What is undefined behavior?
   UB is the execution of code that has not been well defined in C++.
   Results can range from correct,incorrect and inconsistent.

[ANV81]

1. What is a variable in C++?
   A variable in C++ is a named object.

2. What is Definition of a variable?
   A variable is defined as having an object with an identifier which is stored in memory as a value along with its properties.

3. What is Instantiation of a variable?
   Instantiation is the process of creating and assigning a memory address to an object once its variable is executed.

4. What is the difference between an l-value and an r-value?
   (Used Google for this as I didn’t see it anywhere in the linked article. Maybe I’m missed it somehow? Got info from this link: Understanding the meaning of lvalues and rvalues in C++)
   L-values exist as variables and are stored in memory while R-values aren’t. R-values are temporarily assigned and don’t reference any space in memory.

5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
   An uninitialized variable is a variable that hasn’t been assigned a value. Using uninitialized variables can give random results and can be challenging to debug, so it’s best to always initialize variables.

6. What is undefined behaviour?
   Undefined behavior is the execution of code that hasn’t been well defined. The results can be random.