Auto and decltype serve different purposes so they don't map one-to-one. auto is a keyword in C++11 and later that is used for automatic type deduction. The decltype type specifier yields the type of a specified expression. Unlike auto that deduces types based on values being assigned to the variable, decltype deduces the type from an expression passed to it. The value returned by decltype can directly be used to define another variable.auto follows the rules of template parameter deduction. You can read more about these rule at http://en.cppreference.com/w/cpp/language/template_argument_deductionWhile decltype has rules it should follow defined in the standard. Here ... Read More

Auto is a keyword in C++11 and later that is used for automatic type deduction. Type inference or deduction refers to the automatic detection of the data type of an expression in a programming language. It is a feature present in some strongly statically typed languages. For example, you want to create an iterator to iterate over a vector, you can simply use auto for that purpose. example#include #include using namespace std; int main() {    vector arr(10);    for(auto it = arr.begin(); it != arr.end(); it ++) {       cin >> *it;    }    return 0; }In ... Read More

You can initialize a variable using the assignment operator or use its constructor when initializing it. For example,int i = 0; MyClass instance(1, "Hello");It will be automatically initialized ifIt's a class/struct instance in which the default constructor initializes all primitive types; like MyClass instance; You use array initializer syntax, e.g. int a[10] = {} (all zeroed) or int a[10] = {1,2}; (all zeroed except the first two items: a[0] == 1 and a[1] == 2) It is a global/extern variable It is defined static

Type inference or deduction refers to the automatic detection of the data type of an expression in a programming language. It is a feature present in some strongly statically typed languages. In C++, the auto keyword(added in C++ 11) is used for automatic type deduction. For example, you want to create an iterator to iterate over a vector, you can simply use auto for that purpose. Example#include #include using namespace std; int main() {    vector arr(10);        for(auto it = arr.begin(); it != arr.end(); it ++) {       cin >> *it;    }    return 0; ... Read More

If you have statements like −Class Person;This is a forward declaration. It lets the following code know that there is are classes with the name Person. This satisfies the compiler when it sees these names used. Later the linker will find the definition of the classes.

In C++, declaration and definition are often confused. A declaration means (in C) that you are telling the compiler about type, size and in case of function declaration, type and size of its parameters of any variable, or user-defined type or function in your program. No space is reserved in memory for any variable in case of the declaration. The Definition on the other hand means that in additions to all the things that declaration does, space is additionally reserved in memory. You can say "DEFINITION = DECLARATION + SPACE RESERVATION". Following are examples of declarations − extern int ... Read More

To define a variable in  C++, you need to use the following syntax −Syntaxdatatype variable_name;You need to know what type of data is your variable is going to hold and what it will be called. The variable name has constraints on what you can name it. Following are the rules for naming variables −Variable names in C++ can range from 1 to 255 characters.All variable names must begin with a letter of the alphabet or an underscore(_).After the first initial letter, variable names can also contain letters and numbers.  Variable names are case sensitive.No spaces or special characters are allowed.You ... Read More

In C++, declaration and definition are often confused. A declaration means (in C) that you are telling the compiler about type, size and in case of function declaration, type and size of its parameters of any variable, or user-defined type or function in your program. No space is reserved in memory for any variable in case of a declaration.The Definition on the other hand means that in additions to all the things that declaration does, space is additionally reserved in memory. You can say "DEFINITION = DECLARATION + SPACE RESERVATION".Following are examples of declarations −extern int a;       ... Read More

An enumerated type declares an optional type name and a set of zero or more identifiers that can be used as values of the type. Each enumerator is a constant whose type is the enumeration. For example, if you are creating an application that has a fixed number of types for some variable. For example, let's say gender, it can be of three types male, female and others. You can define and use an enum like −#include using namespace std; enum Gender {MALE, FEMALE, OTHERS}; int main() {    Gender gen = Gender.FEMALE;    return 0; }By default, the value ... Read More

The equality operators in C++ are is equal to(==) and is not equal to(!=). They do the task as they are named. The binary equality operators compare their operands for strict equality or inequality. The equality operators, equal to (==) and not equal to (!=), have lower precedence than the relational operators, but they behave similarly. The result type for these operators is bool.The equal-to operator (==) returns true (1) if both operands have the same value; otherwise, it returns false (0). The not-equal-to operator (!=) returns true if the operands do not have the same value; otherwise, it returns ... Read More