Stack and Queue in C++

Introduction to stacks and queues in C

Stacks and queues are commonly used data structures in C, and they are widely used in programs. This article will introduce the concepts, usage and application scenarios of stacks and queues in detail.

1. The concept of stack

Stack is a linear data structure, which has the characteristics of "first in, last out". In the stack, the data pushed into the stack is closer to the bottom of the stack; the data pushed into the stack later is closer to the top of the stack.

The main operations of the stack are push and pop. Pushing is to add data to the stack, and popping is to delete data from the stack. The stack also has two important special operations: viewing the top element of the stack (top) and determining whether the stack is empty (empty).

The application scenarios of the stack are very wide. For example, the use of the stack is involved when calling functions. When a function is called, its parameters, local variables and other information will be pushed onto the stack. When the function execution ends, this information will be popped from the stack and restored to the state before the function call.

2. The concept of queue

Queue (Queue) is also a linear data structure, which has the characteristics of "first in, first out". In the queue, the data that is queued earlier is closer to the head of the queue; the data that is queued later is closer to the end of the queue.

The main operations of the queue are enqueue and dequeue. Entering the queue means adding data to the end of the queue, while dequeuing means deleting data from the head of the queue. The queue also has two important special operations: viewing the head element (front) and determining whether the queue is empty (empty).

Queues are also widely used. For example, in process scheduling in the operating system, queues can be used to save processes waiting to be executed. When system resources are free, a process is taken out from the head of the queue and executed until all tasks are completed.

3. Application examples of stacks and queues

1. Bracket matching

In programming, it is often necessary to determine whether the brackets in a string match. For example, when writing a Python program, if you need to check whether the code block is indented correctly, you can use the stack to achieve this.

The specific implementation method is to traverse every character in the string and push it onto the stack when encountering a left bracket. When a right parenthesis is encountered, the top element of the stack is popped for matching. If the match is successful, continue traversing; otherwise, an error message is returned.

2. Process Scheduling

In the operating system, it is necessary to achieve unified scheduling and coordination of processes. At this time, you can use a queue to store processes waiting for execution, and the operating system determines the priority and execution order.

The specific implementation method is to abstract each process into a data structure, including process number, priority and other information. Put these processes into a queue, and then execute the processes in the queue in sequence. When a process completes its task, it will be popped out of the queue until the queue is empty.

4. Implementation of stacks and queues in C

In C, you can use the container classes provided by the standard library to implement stacks and queues.

1. Implementation of stack

The stack can be implemented using the container class std::stack.

std::stack is a template class that requires specifying the element type and underlying container type. When the underlying container type is not specified, std::deque is used as the underlying container by default.

The following is a simple stack implementation example:

#include <iostream>
#include <stack>

int main() {
    std::stack<int> s;

    s.push(1);
    s.push(2);
    s.push(3);

    std::cout << s.top() << std::endl; // 输出3

    s.pop();

    std::cout << s.top() << std::endl; // 输出2

    while (!s.empty()) {
        s.pop();
    }

    return 0;
}

2. Queue implementation

The queue can be implemented using the container class std::queue.

std::queue is also a template class and needs to specify the element type and underlying container type. When the underlying container type is not specified, std::deque is used as the underlying container by default.

The following is a simple queue implementation example:

#include <iostream>
#include <queue>

int main() {
    std::queue<int> q;

    q.push(1);
    q.push(2);
    q.push(3);

    std::cout << q.front() << std::endl; // 输出1

    q.pop();

    std::cout << q.front() << std::endl; // 输出2

    while (!q.empty()) {
        q.pop();
    }

    return 0;
}

Summary

As can be seen from the above introduction, stacks and queues are very practical data structures that can help We solve a lot of real problems. In programming, mastering the usage and implementation principles of these two data structures can improve the efficiency and reliability of the program.

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