Variables in C++ - Reading Assignment

C++ Programming
#162

  1. What is a variable in C++?
    A C++ variable is an object that represents an area of storage such as memory and holds a value and associated properties.

  2. What is Definition of a variable?
    When a variable is defined, the compiler will determine where the object will be placed in memory. This allows the programmer to interact with the value stored in memory via the object rather than the memory address.

  3. What is Instantiation of a variable?
    Instantiation is the creation and memory address assignment of a variable at runtime.

  4. What is the difference between an l-value and an r-value?
    The l and the r stand for left and right respectively and represent the side of the expression the values are expected to appear on. L-values persist in memory wheres r-values are only assigned temporary space. In some instances you can find a l-value in an r-value context, but you will never find an r-value in an l-value context.

  5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
    An uninitialised variable is one that has not yet been given a value. If it is subsequently used, the compiler will allocate it to a memory space and whatever value resides in that space. Therefore, it is not possible to determine what value will be returned from an uninitialised variable.

  6. What is undefined behaviour?
    Undefined behaviour is the result of executing code whose behaviour is not well defined by the C++ language. Symptoms can vary and you may find that your program;
    a. produces different results every time it is run.
    b. consistently produces the same incorrect result.
    c. behaves inconsistently (sometimes produces the correct result, sometimes not).
    d. seems like its working but produces incorrect results later in the program.
    e. crashes, either immediately or later.
    f. works on some compilers but not others.
    g. works until you change some other seemingly unrelated code.
    h. works as intended.

#163

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#164
  1. It’s a named object
  2. It’s the region of storage holding data.
  3. Creating a variable and assigning it a memory address.
  4. L-values are on the left side of a statement and R-values are on the right. L values are constant and are held in a memory address whereas R-values are temporary and can be overwritten. X = 5, but 5 != X
  5. X{} x doesn’t have a value right now and will give us unexpected results different times we use the program.
  6. It’s exactly as it sounds. We don’t know what will happen to the program because it’s operating outside of the rules of the C++ language. Sometimes it might work, sometimes not, works for some people but not others etc.
#165

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

  2. What is Definition of a variable?
    In order to create variables we use a special kind of declaration statement called definition.

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

  4. What is the difference between an l-value and an r-value?
    An l-value has a persistent address and r-valur is not associated with a persistent memory address.

  5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
    An uninitialized variable was not given a known value. The compiler will assign a random space in the memory and it can change every time we run and compile the code.

  6. What is undefined behaviour?
    Undefined behaviour is unpredictable and random, because it results from uninitialized variables.

#166
  1. a named object
  2. a declaration of a varaible without assignement
  3. a reservation of memory in RAM at runtime
  4. I-value has an address in memory and can accessed via the address; R-Value can not accessed via an adress.
  5. a defined variable where no value was accessed; using it leads to an unexpected behavior
  6. crash of programm, undefined outpust, may work may not etc.
#167

1.A named object is called variable.
2.Definition of variable - it is not consistent or having fixed patterns; liable to change.
3. Instantiation of a variable is the process when the object will be created and assigned a memory address. Variables must be instantiated before they can be used to store values.
4. I-value has a persisten address, r-value has not.
5.It has not been given a known value, can cause unexpected behavior.
6. When software doesn’t work properly or work differently every time.

#168

1 )
A variable is a named object. The name of the object is called identifier. An object is a region of storage (usually memory) that has a value and other associated properties

A definition of a variable is a piece of code that assigns a variable named “something”, to a type (f.e. int)

define a variable named x, of type int

When the program is run (called runtime), the variable will be instantiated. Instantiation means the object will be created and assigned a memory address. Variables must be instantiated before they can be used to store values.

lvalue is anything whose address is accessible. It means we can take address of lvalue using & operator. f.E: int x = 1; x is an lvalue because we can access the address of x
Rvalue is anything that is not lvalue. It means we cannot take address of rvalue and it also don’t persist beyond the single expression. f.e: int x = 1; Here you can not take the address of 1 Therefore, 1 is not a lvalue and hence it 1 is rvalue .

6,7)
To create a variable without an initial value, simply don’t include an initial value:

This creates an uninitialized int
int i;

The value in an uninitialized variable can be anything – it is unpredictable, and may be different every time the program is run. Reading the value of an uninitialized variable is undefined behaviour – which is always a bad idea. It has to be initialized with a value before you can use it.

#169

  1. What is a variable in C++?
    An object in memory that has a value (and other properties).

  2. What is Definition of a variable?
    Declaration of the name and type of the variable

  3. What is Instantiation of a variable?
    At runtime when the variable is created and assigned a memory address.

  4. What is the difference between an l-value and an r-value?
    l-value is assigned to an address in memory. an r-value is the opposite, a temporary value.

  5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
    A variable that has assigned memory but no value has been set yet. So the value will be the value of that unassigned memory, which in practice can be any value.

  6. What is undefined behaviour?
    Behaviour that is not defined by C++. it can crash, show different results each time, or shows other inconsistencies. Basically all stuff you don’t want to happen to your program.

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#170

1 A named object is called a variable.
2 A declaration statement used to create a variable is called a definition.
3 Instantiation is a fancy word that means the object will be created and assigned a memory address.
4 l-value is the assignee, r-value is an expression that determines the value to assign
5 A declared variable whose value in the memory address has not yet been initialized. using such variables can lead to undefined behavior.
6 Undefined behavior is the result of executing code whose behavior is not well defined by the language.

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#171
  1. A C++ variable is a named object (which is a region of storage that has a value and other associated properties). It can be
  2. The definition of a variable is a special kind of declaration that defines the variable.
  3. Instantiation of a variable means, that at runtime, the variable is created and assigned memory space.
  4. An l-value is an object that has a name, which persists beyond a single expression. An r-value is a temporary value that does not persist beyond the expression that uses it.
  5. An uninitialized variable is a variable in memory that does not have a value assigned. Using an uninitialized variable can cause undefined behavior.
  6. Undefined behavior is behavior that is unpredictable.
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#172

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#173

1 a named object
2 a definition is a declaration statement that creates a variable.
3 this means that an object is created and assigned a memory address.
4 rvalue is something that could only go on the Right-hand side of an assignment, as opposed to an lvalue which could go on the left-hand side of an assignment.
5 a variable that has not been given a memory address and can have undefined behaviour.
6 when code in not well defined.

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#174

1. What is a variable in C++?

An object is a region of storage (usually memory) that has a value and other associated properties.

Objects can be named or unnamed (anonymous). A named object is called a variable , and the name of the object is called an identifier .

2. What is Definition of a variable?

A definition is a special kind of declaration statement used to create a variable.

3. What is Instantiation of a variable?

When the program is run (called runtime ), the variable will be instantiated. Instantiation means the object will be created and assigned a memory address. Variables must be instantiated before they can be used to store values.

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

An lvalue ( locator value ) represents an object that occupies some identifiable location in memory (i.e. has an address).

rvalues are defined by exclusion, by saying that every expression is either an lvalue or an rvalue . Therefore, from the above definition of lvalue , an rvalue is an expression that does not represent an object occupying some identifiable location in memory.

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

Unitialized means the object has not been given a known value. Therefore, an object that is not initialized but is then assigned a value is no longer uninitialized.

Most modern compilers will attempt to detect if a variable is being used without being given a value. If they are able to detect this, they will generally issue a compile-time error.

Using uninitialized variables is one of the most common mistakes that novice programmers make, and unfortunately, it can also be one of the most challenging to debug.

6. What is undefined behaviour?

Undefined behavior is the result of executing code whose behavior is not well defined by the C++ language. In this case, the C++ language doesn’t have any rules determining what happens if you use the value of a variable that has not been given a known value. Consequently, if you actually do this, undefined behavior will result.

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#175

Quiz time

Question #1

What is data?

In computing, data is any information that can be moved, processed, or stored by a computer.

Question #2

What is a value?

A single piece of data, stored in memory somewhere, is called a value .

Question #3

What is a variable?

Objects can be named or unnamed (anonymous). A named object is called a variable.

Question #4

What is an identifier?

The name of an object is called an identifier .

Question #5

What is a type?

A data type (more commonly just called a type ) tells the compiler what type of value (e.g. a number, a letter, text, etc…) a variable will store.

Question #6

What is an integer?

An integer is a number that can be written without a fractional component, such as 4, 27, 0, -2, or -12.

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#176

  1. What is a variable in C++? the user defined name (of a given type) that can store value.

  2. What is Definition of a variable? To define a var, is when you include the variable type, ie. int, double, etc. The var is then allocated a memory address that can hold data and be referenced.

  3. What is Instantiation of a variable? It is when the var has been activated at run time.

  4. What is the difference between an l-value and an r-value? An l-value always has a defined region of storage, so you can take its address. An r-value represents a value and does not necessarily have any storage associated with it.

  5. What is an uninitialized variable and what kind of behavior can you expect from such a variable? Its when a var has been declared but not assigned a value. Using such vars can result in it obtaining whatever garbage value may be at that memory address, hence unexpected results.

  6. What is undefined behaviour? Code that performs tasks outside the C++ standard, which may still compile and execute but may, for example, reference deleted objects, or point to array addresses beyond existing parameters.

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#177

  1. A variable is used to store any piece of data.

  2. The place where you create the space in memory for your variable is called the definition.

  3. When you store a value into a variable, that is called Instantiation.

  4. L-values persist in memory and r-values do not.

  5. An uninitialized variable is one that has a place in memory, but it does not yet have a value assigned to it. Your program will throw an error if you try to use that variable other than to instantiate it.

  6. Undefined behavior is a nice way to say you have a bug in your code. Your program doesn’t work the way you intend it to.

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#178
  1. A named location in memory where data can be stored.
  2. Defining the name and type of a variable.
  3. Assigning a value to a variable.
  4. l-value is a variable with an address. It means left-value because it always occurs on the left side of a statement and therefore has a value assigned to it.
    r-values occur on the right side in statements and are values assigned to l-values.
  5. A variable that has not been assigned a value, it takes on a garbage value by default. It will lead to unpredictable behavior.
  6. Executing code whose behavior is not well defined. E.g. using values from an uninitialized variable.
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#179

  1. What is a variable in C++?
    it represents a location of sotrage (memory) that stores a value and other properties

  2. What is Definition of a variable?
    it’s a statement that creates a variable

  3. What is Instantiation of a variable?
    it means that an object will be created and assigned a memory address

  4. What is the difference between an l-value and an r-value?
    lvalues do not change address, rvalues can be relocated in memory

  5. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
    it’s a variable that was not assigned a value when it was created so its initial value depends on wathever information was stored at the memory location assigned to the variable

  6. What is undefined behaviour?
    is what results of executing code whose behavior is not well defined by the language

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#180
  1. What is a variable in C++?

In C++, variables are named objects (data structures in memory) that can store data value.

  1. What is Definition of a variable?

Definition of variable is giving it the name and the type in which it is going to be read by compiler. eg. int x; where x is variable’s name and int is variable’s type

  1. What is Instantiation of a variable?

Instantiation of a variable is process of creating named object and assigning it to a memory address. Without Instantiation variables cannot store values.

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

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

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

Uninitialized variable is a variable that has not been given a known value through initialization or assignment. Using uninitialized variables can lead to undefined behavior with unexpected results (we can’t know if program will print any value and what this value may be).

  1. What is undefined behaviour?

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

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#181
  1. What is a variable in C++?
  • A variable in C++ is a named object, but the name of the actual object is known as the identifier
  1. What is Definition of a variable?
  • A definition of a variable is a declaration statement, which is used to create the variable
  1. What is Instantiation of a variable?
  • Instantiation of a variable is when the object will be created and assigned a memory address
  1. What is the difference between an l-value and an r-value?
  • L-values have a persistent place in memory whereas r-values are discarded at the end of a statement. Because of this, they do not need a memory address
  1. What is an uninitialized variable and what kind of behaviour can you expect from such a variable?
  • An uninitialized variable is a variable that has not been given a known value. When using an uninitialized variable, that variable will be set to a default value.
  1. What is undefined behaviour?
  • Undefined behaviour is the result of executing code whose behaviour is not well defined by the C++ language
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