The usefulness of the 'Hello World' programs shown in the previous chapter is rather questionable. We had to write several lines of code, compile them, and then execute the resulting program, just to obtain the result of a simple sentence written on the screen. It certainly would have been much faster to type the output sentence ourselves.
However, programming is not limited only to printing simple texts on the screen. In order to go a little further on and to become able to write programs that perform useful tasks that really save us work, we need to introduce the concept of variables.
Let's imagine that I ask you to remember the number 5, and then I ask you to also memorize the number 2 at the same time. You have just stored two different values in your memory (5 and 2). Now, if I ask you to add 1 to the first number I said, you should be retaining the numbers 6 (that is 5+1) and 2 in your memory. Then we could, for example, subtract these values and obtain 4 as result.
The whole process described above is a simile of what a computer can do with two variables. The same process can be expressed in C++ with the following set of statements:
Obviously, this is a very simple example, since we have only used two small integer values, but consider that your computer can store millions of numbers like these at the same time and conduct sophisticated mathematical operations with them.
We can now define variable as a portion of memory to store a value.
Each variable needs a name that identifies it and distinguishes it from the others. For example, in the previous code the variable names were a, b, and result, but we could have called the variables any names we could have come up with, as long as they were valid C++ identifiers.

I always though that if I declare these three variables that they will all have the value 0. Int column, row, index = 0; But I find that only index equals zero & the others are junk like 844553 & 2423445. How can I initialise all these variables to zero without declaring each variable on a new line? Dec 12, 2019  A C program might contain more than one compilation unit. To declare an entity that is defined in a separate compilation unit, use the extern keyword. The information in the declaration is sufficient for the compiler, but if the definition of the entity cannot be found in the linking step, then the linker will raise an error. Feb 16, 2018 Do static variables get initialized in a default constructor in java? Can we declare a static variable within a method in java? Are the values of static variables stored when an object is serialized in Java? Where and how to use to static variables in android studio? How to swap variables with destructuring in JavaScript? When a variable is assigned a symbolic name like 'employeepayrollid,' the compiler or interpreter can work out where to store the variable in memory. Variable Types When you declare a variable in a program, you specify its type, which can be chosen from integral, floating point, decimal, boolean.

May 31, 2017  Scope of Variables in C In general, the scope is defined as the extent up to which something can be worked with. In programming also the scope of a variable is defined as the extent of the program code within which the variable can we accessed or declared or worked with.

Identifiers

A valid identifier is a sequence of one or more letters, digits, or underscore characters (_). Spaces, punctuation marks, and symbols cannot be part of an identifier. In addition, identifiers shall always begin with a letter. They can also begin with an underline character (_), but such identifiers are -on most cases- considered reserved for compiler-specific keywords or external identifiers, as well as identifiers containing two successive underscore characters anywhere. In no case can they begin with a digit.
C++ uses a number of keywords to identify operations and data descriptions; therefore, identifiers created by a programmer cannot match these keywords. The standard reserved keywords that cannot be used for programmer created identifiers are:
alignas, alignof, and, and_eq, asm, auto, bitand, bitor, bool, break, case, catch, char, char16_t, char32_t, class, compl, const, constexpr, const_cast, continue, decltype, default, delete, do, double, dynamic_cast, else, enum, explicit, export, extern, false, float, for, friend, goto, if, inline, int, long, mutable, namespace, new, noexcept, not, not_eq, nullptr, operator, or, or_eq, private, protected, public, register, reinterpret_cast, return, short, signed, sizeof, static, static_assert, static_cast, struct, switch, template, this, thread_local, throw, true, try, typedef, typeid, typename, union, unsigned, using, virtual, void, volatile, wchar_t, while, xor, xor_eq

Specific compilers may also have additional specific reserved keywords.
Very important: The C++ language is a 'case sensitive' language. That means that an identifier written in capital letters is not equivalent to another one with the same name but written in small letters. Thus, for example, the RESULT variable is not the same as the result variable or the Result variable. These are three different identifiers identifiying three different variables.

Fundamental data types

The values of variables are stored somewhere in an unspecified location in the computer memory as zeros and ones. Our program does not need to know the exact location where a variable is stored; it can simply refer to it by its name. What the program needs to be aware of is the kind of data stored in the variable. It's not the same to store a simple integer as it is to store a letter or a large floating-point number; even though they are all represented using zeros and ones, they are not interpreted in the same way, and in many cases, they don't occupy the same amount of memory.
Fundamental data types are basic types implemented directly by the language that represent the basic storage units supported natively by most systems. They can mainly be classified into:

• Character types: They can represent a single character, such as 'A' or '$'. The most basic type is char, which is a one-byte character. Other types are also provided for wider characters.
• Numerical integer types: They can store a whole number value, such as 7 or 1024. They exist in a variety of sizes, and can either be signed or unsigned, depending on whether they support negative values or not.
• Floating-point types: They can represent real values, such as 3.14 or 0.01, with different levels of precision, depending on which of the three floating-point types is used.
• Boolean type: The boolean type, known in C++ as bool, can only represent one of two states, true or false.

Here is the complete list of fundamental types in C++:

Group	Type names*	Notes on size / precision
Character types	char	Exactly one byte in size. At least 8 bits.
	char16_t	Not smaller than char. At least 16 bits.
	char32_t	Not smaller than char16_t. At least 32 bits.
	wchar_t	Can represent the largest supported character set.
Integer types (signed)	signed char	Same size as char. At least 8 bits.
	signedshortint	Not smaller than char. At least 16 bits.
	signedint	Not smaller than short. At least 16 bits.
	signedlongint	Not smaller than int. At least 32 bits.
	signedlong longint	Not smaller than long. At least 64 bits.
Integer types (unsigned)	unsigned char	(same size as their signed counterparts)
	unsigned shortint
	unsignedint
	unsigned longint
	unsigned long longint
Floating-point types	float
	double	Precision not less than float
	long double	Precision not less than double
Boolean type	bool
Void type	void	no storage
Null pointer	decltype(nullptr)

* The names of certain integer types can be abbreviated without their signed and int components - only the part not in italics is required to identify the type, the part in italics is optional. I.e., signed short int can be abbreviated as signed short, short int, or simply short; they all identify the same fundamental type.
Within each of the groups above, the difference between types is only their size (i.e., how much they occupy in memory): the first type in each group is the smallest, and the last is the largest, with each type being at least as large as the one preceding it in the same group. Other than that, the types in a group have the same properties.
Note in the panel above that other than char (which has a size of exactly one byte), none of the fundamental types has a standard size specified (but a minimum size, at most). Therefore, the type is not required (and in many cases is not) exactly this minimum size. This does not mean that these types are of an undetermined size, but that there is no standard size across all compilers and machines; each compiler implementation may specify the sizes for these types that fit the best the architecture where the program is going to run. This rather generic size specification for types gives the C++ language a lot of flexibility to be adapted to work optimally in all kinds of platforms, both present and future.
Type sizes above are expressed in bits; the more bits a type has, the more distinct values it can represent, but at the same time, also consumes more space in memory:

Size	Unique representable values	Notes
8-bit	256	= 28
16-bit	65 536	= 216
32-bit	4 294 967 296	= 232 (~4 billion)
64-bit	18 446 744 073 709 551 616	= 264 (~18 billion billion)

For integer types, having more representable values means that the range of values they can represent is greater; for example, a 16-bit unsigned integer would be able to represent 65536 distinct values in the range 0 to 65535, while its signed counterpart would be able to represent, on most cases, values between -32768 and 32767. Note that the range of positive values is approximately halved in signed types compared to unsigned types, due to the fact that one of the 16 bits is used for the sign; this is a relatively modest difference in range, and seldom justifies the use of unsigned types based purely on the range of positive values they can represent.
For floating-point types, the size affects their precision, by having more or less bits for their significant and exponent.
If the size or precision of the type is not a concern, then char, int, and double are typically selected to represent characters, integers, and floating-point values, respectively. The other types in their respective groups are only used in very particular cases.

Declare Variable Java

The properties of fundamental types in a particular system and compiler implementation can be obtained by using the numeric_limits classes (see standard header '><limits>). If for some reason, types of specific sizes are needed, the library defines certain fixed-size type aliases in header '><cstdint>.
The types described above (characters, integers, floating-point, and boolean) are collectively known as arithmetic types. But two additional fundamental types exist: void, which identifies the lack of type; and the type nullptr, which is a special type of pointer. Both types will be discussed further in a coming chapter about pointers.
C++ supports a wide variety of types based on the fundamental types discussed above; these other types are known as compound data types, and are one of the main strengths of the C++ language. We will also see them in more detail in future chapters.

Declaration of variables

C++ is a strongly-typed language, and requires every variable to be declared with its type before its first use. This informs the compiler the size to reserve in memory for the variable and how to interpret its value. The syntax to declare a new variable in C++ is straightforward: we simply write the type followed by the variable name (i.e., its identifier). For example:

These are two valid declarations of variables. The first one declares a variable of type int with the identifier a. The second one declares a variable of type float with the identifier mynumber. Once declared, the variables a and mynumber can be used within the rest of their scope in the program.
If declaring more than one variable of the same type, they can all be declared in a single statement by separating their identifiers with commas. For example:
This declares three variables (a, b and c), all of them of type int, and has exactly the same meaning as:

To see what variable declarations look like in action within a program, let's have a look at the entire C++ code of the example about your mental memory proposed at the beginning of this chapter:
Don't be worried if something else than the variable declarations themselves look a bit strange to you. Most of it will be explained in more detail in coming chapters.

Initialization of variables

When the variables in the example above are declared, they have an undetermined value until they are assigned a value for the first time. But it is possible for a variable to have a specific value from the moment it is declared. This is called the initialization of the variable.
In C++, there are three ways to initialize variables. They are all equivalent and are reminiscent of the evolution of the language over the years:
The first one, known as c-like initialization (because it is inherited from the C language), consists of appending an equal sign followed by the value to which the variable is initialized:
type identifier = initial_value;
For example, to declare a variable of type int called x and initialize it to a value of zero from the same moment it is declared, we can write:

A second method, known as constructor initialization (introduced by the C++ language), encloses the initial value between parentheses (()):
type identifier (initial_value);
For example:
Finally, a third method, known as uniform initialization, similar to the above, but using curly braces ({}) instead of parentheses (this was introduced by the revision of the C++ standard, in 2011):
type identifier {initial_value};
For example:

All three ways of initializing variables are valid and equivalent in C++.

Type deduction: auto and decltype

When a new variable is initialized, the compiler can figure out what the type of the variable is automatically by the initializer. For this, it suffices to use auto as the type specifier for the variable:

Here, bar is declared as having an auto type; therefore, the type of bar is the type of the value used to initialize it: in this case it uses the type of foo, which is int.
Variables that are not initialized can also make use of type deduction with the decltype specifier:
Here, bar is declared as having the same type as foo.
auto and decltype are powerful features recently added to the language. But the type deduction features they introduce are meant to be used either when the type cannot be obtained by other means or when using it improves code readability. The two examples above were likely neither of these use cases. In fact they probably decreased readability, since, when reading the code, one has to search for the type of foo to actually know the type of bar.

Introduction to strings

Fundamental types represent the most basic types handled by the machines where the code may run. But one of the major strengths of the C++ language is its rich set of compound types, of which the fundamental types are mere building blocks.
An example of compound type is the string class. Variables of this type are able to store sequences of characters, such as words or sentences. A very useful feature!
A first difference with fundamental data types is that in order to declare and use objects (variables) of this type, the program needs to include the header where the type is defined within the standard library (header <string>):

As you can see in the previous example, strings can be initialized with any valid string literal, just like numerical type variables can be initialized to any valid numerical literal. As with fundamental types, all initialization formats are valid with strings:
Strings can also perform all the other basic operations that fundamental data types can, like being declared without an initial value and change its value during execution:

Note: inserting the endl manipulator ends the line (printing a newline character and flushing the stream).
The string class is a compound type. As you can see in the example above, compound types are used in the same way as fundamental types: the same syntax is used to declare variables and to initialize them.
For more details on standard C++ strings, see the string class reference.

Previous: Structure of a program

Index

Next: Constants

A variable in simple terms is a storage place which has some memory allocated to it. Basically, a variable used to store some form of data. Different types of variables require different amounts of memory, and have some specific set of operations which can be applied on them.

Variable Declaration:
A typical variable declaration is of the form:

C++ Declaring Global Variables

A variable name can consist of alphabets (both upper and lower case), numbers and the underscore ‘_’ character. However, the name must not start with a number.

Difference b/w variable declaration and definition
Variable declaration refers to the part where a variable is first declared or introduced before its first use. Vip producer vst crack. Variable definition is the part where the variable is assigned a memory location and a value. Most of the times, variable declaration and definition are done together.

See the following C program for better clarification: Auto tune efx 3toorrent.

intmain() // declaration and definition of variable 'a123' // This is also both declaration and definition as 'b' is allocated // memory and assigned some garbage value. int_c, _d45, e; // Let us print a variable }

Output:

Is it possible to have separate declaration and definition?
It is possible in case of extern variables and functions. See question 1 of this for more details.

Keywords are specific reserved words in C each of which has a specific feature associated with it. Almost all of the words which help us use the functionality of the C language are included in the list of keywords. So you can imagine that the list of keywords is not going to be a small one!

There are a total of 32 keywords in C:

Most of these keywords have already been discussed in the various sub-sections of the C language, like Data Types, Storage Classes, Control Statements, Functions etc.

Let us discuss some of the other keywords which allow us to use the basic functionality of C:

const: const can be used to declare constant variables. Constant variables are variables which, when initialized, can’t change their value. Or in other words, the value assigned to them cannot be modified further down in the program.
Syntax:

Note: Constant variables must be initialized during their declaration. const keyword is also used with pointers. Please refer the const qualifier in C for understanding the same.

How To Declare Variables In Dev C Pdf

extern: extern simply tells us that the variable is defined elsewhere and not within the same block where it is used. Basically, the value is assigned to it in a different block and this can be overwritten/changed in a different block as well. So an extern variable is nothing but a global variable initialized with a legal value where it is declared in order to be used elsewhere. It can be accessed within any function/block. Also, a normal global variable can me made extern as well by placing the ‘extern’ keyword before its declaration/definition in any function/block. This basically signifies that we are not initializing a new variable but instead we are using/accessing the global variable only. The main purpose of using extern variables is that they can be accessed between two different files which are part of a large program.
Syntax:

static: static keyword is used to declare static variables, which are popularly used while writing programs in C language. Static variables have a property of preserving their value even after they are out of their scope! Hence, static variables preserve the value of their last use in their scope. So we can say that they are initialized only once and exist till the termination of the program. Thus, no new memory is allocated because they are not re-declared. Their scope is local to the function to which they were defined. Global static variables can be accessed anywhere within that file as their scope is local to the file. By default, they are assigned the value 0 by the compiler.
Syntax:

void: void is a special data type. But what makes it so special? void, as it literally means, is an empty data type. It means it has nothing or it holds no value. For example, when it is used as the return data type for a function it simply represents that the function returns no value. Similarly, when its added to a function heading, it represents that the function takes no arguments.
Note: void also has a significant use with pointers. Please refer to the void pointer in C for understanding the same.

typedef: typedef is used to give a new name to an already existing or even a custom data type (like a structure). It comes in very handy at times, for example in a case when the name of the structure defined by you is very long or you just need a short-hand notation of a per-existing data type.

Let’s implement the keywords which we have discussed above. Take a look at the following code which is a working example to demonstrate these keywords:

externintx = 9; // declaring and initializing a global variable // the default value of a global variable which is 0 // using typedef to give a short name to long long int // very convenient to use now due to the short name // function which prints square of a no. and which has void as its voidcalSquare(intarg) printf('The square of %d is %d',arg,arg*arg); // Here void means function main takes no parameters { // declaring a constant variable, its value cannot be modified charb = 'G'; // telling the compiler that the variable z is an extern variable // and has been defined elsewhere (above the main function) printf('This is the value of the constant variable 'a': %d',a); printf('b' is a char variable. Its value is %c',b); printf('c' is a long long int variable. Its value is %lld',c); printf('These are the values of the extern variables 'x' and 'z' x=2; // value of extern variable z modified // printing the modified values of extern variables 'x' and 'z' printf('These are the modified values of the extern variables' printf('The value of static variable 'y' is NOT initialized to 5 after the ' 'first iteration! See for yourself :)'); while(x > 0) staticinty = 5; // printing value at each iteration x--; calSquare(5); printf('Bye! See you soon. :)'); return0;

Output:

C++ Declare Variable Without Constructing