Variable and constant are two commonly used mathematical concepts. Simply put, a variable is a value that is changing or that have the ability to change. A constant is a value which remains unchanged.For example, if you have a program that has a list of 10 radii and you want to calculate the area for all of these circles. To find the area of these circles, you'll write a program that will have a variable that will store the value of PI and this value will not change throughout the program. Such values can be declared as a constant.In the ... Read More

There are no types of constants in C++. It's just that you can declare any data type in C++ to be a constant. If a variable is declared as constant using the const keyword, you cannot reassign its value. Example#include using namespace std; int main() {    const int i = 5;    // Now all of these operations are illegal and    // will cause an error:    i = 10;    i *= 2;    i++;    i--;    //...    return 0; }

You can define constants in C++ by adding the const qualifier before the declaration of the variable. Example#include using namespace std; int main() {    const int x = 9;    x = 0;    return 0; }This will define the constant variable x. But it will throw an error as we are trying to rewrite the value of a constant.

To declare a variable, you need to know what data type it is going to be of and what its name would be. 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 cannot use a C++ keyword (a reserved word) as a variable name.Here ... Read More

To declare a variable, you need to know what data type it is going to be of and what its name would be. 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 cannot use a C++ keyword (reserved word) as a variable name.Here are ... Read More

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; }In the ... Read More

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