std::deque (short for double-ended queue) is a container in C++ that allows fast insertion and deletion at both ends. It’s part of the Standard Template Library (STL).
contiguous: touching or next to something
#include <deque>
#include <iostream>
using namespace std;
int main() {
deque<int> dq;
// Add elements
dq.push_back(10); // [10]
dq.push_front(20); // [20, 10]
// Access elements
cout << dq.front() << endl; // 20
cout << dq.back() << endl; // 10
cout << dq[1] << endl; // 10
// Remove elements
dq.pop_front(); // [10]
dq.pop_back(); // []
return 0;
}
dq[1] means "give me the element at index 1".Since C++ uses zero-based indexing,
dq[0] is the first element, and dq[1] is the second element.intimidate somebody (into something/into doing something) to frighten or threaten somebody so that they will do what you want
In C++, template is used to define generic functions or classes, while typename clarifies that a dependent name inside a template refers to a type.
template <typename T>
T add(T a, T b) {
return a + b;
}
enum class in C++ is a strongly typed enumeration introduced in C++11. It improves upon traditional enum by providing better type safety and scoping.
#include <iostream>
using namespace std;
enum class Color { Red, Green, Blue };
enum class Fruit { Apple, Banana, Orange };
int main() {
Color c = Color::Red;
Fruit f = Fruit::Apple;
// Scoped access
cout << (c == Color::Red) << endl; // true
cout << (f == Fruit::Banana) << endl; // false
// No implicit conversion to int
// int x = c; // ❌ Error
// Explicit cast required
int x = static_cast<int>(Color::Green); // ✅ Works
cout << x << endl; // prints 1
}
In C++, the operator == is the equality comparison operator.
It checks whether two values are equal.
Returns a boolean (
true or false).The symbol :: in C++ is called the scope resolution operator. It’s used to specify the scope in which a name (variable, function, class, etc.) is defined.
Main Uses of ::
1. Accessing Global Variables
If a local variable shadows a global one, :: lets you access the global version:
#include <iostream>
using namespace std;
int x = 10; // global
int main() {
int x = 20; // local
cout << x << endl; // prints 20
cout << ::x << endl; // prints 10 (global x)
}
2. Accessing Class Members
Used to define or access members outside the class body:
class MyClass {
public:
static int value;
void show();
};
int MyClass::value = 42; // define static member
void MyClass::show() { // define member function
std::cout << "Value = " << value << std::endl;
}
3. Accessing Namespaces
Used to access functions, classes, or variables inside a namespace:
#include <iostream>
namespace Math {
int add(int a, int b) { return a + b; }
}
int main() {
std::cout << Math::add(3, 4) << std::endl; // 7
}
4. Enumerations
With enum class, you must use :: to access enumerators:
enum class Color { Red, Green, Blue };
Color c = Color::Red; // scoped access
In programming, a dummy value usually means a placeholder value that doesn’t carry real meaning but is used temporarily.
#include is a C++ standard library header that provides a collection of utility functions, classes, and templates commonly used in generic programming.
Here is one of the most important components:
std::pair
- A simple container that holds two values.
- Useful for returning two results from a function or storing key-value pairs.
for (initialization; condition; update) {
// code to execute repeatedly
}
Let’s combine a for loop with a switch statement in C++. This is a common pattern when you want to iterate through values and perform different actions depending on the case.
#include <iostream>
using namespace std;
int main() {
// Loop from 1 to 5
for (int i = 1; i <= 5; i++) {
switch (i) {
case 1:
cout << "Case 1: Hello" << endl;
break; // exit switch
case 2:
cout << "Case 2: World" << endl;
break;
case 3:
cout << "Case 3: Foo" << endl;
break;
case 4:
cout << "Case 4: Bar" << endl;
break;
default:
cout << "Default case: i = " << i << endl;
break;
}
}
return 0;
}
- The for loop runs from i = 1 to i = 5.
- Each iteration enters the switch block.
- The case labels match specific values of i.
- The break ensures the program exits the switch after executing one case (otherwise it would “fall through” to the next case).
- The default handles values not explicitly (clearly or directly, so that the meaning is easy to understand) listed in cases.
Case 1: Hello
Case 2: World
Case 3: Foo
Case 4: Bar
Default case: i = 5
- break inside switch only exits the switch, not the for loop.
- If you want to exit the entire loop from inside a switch, you can use break with a label (C++20) or goto, or simply return if inside main.
for (const auto& op : operations) {
// use op here
}
- operations → a container (like std::vector, std::deque, std::list, etc.).
- op → each element in the container, one at a time.
- auto& → deduces the element type automatically and binds it by reference (so no copy is made).
- const → ensures you cannot modify the element inside the loop.
if (!schedule.empty())
- schedule → some container (like std::vector, std::deque, std::list, std::map, etc.).
- .empty() → a member function that returns true if the container has no elements, false otherwise.
- ! → logical NOT operator, flips the result.
So the condition means:
“If schedule is NOT empty, then execute the following block.
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