Hello look this its better :
#include <iostream>
#include <fstream>
#include <vector>
#include <string>

class Queue {
public:
    explicit Queue(int max_size) : size_(0), max_size_(max_size), head_(0), tail_(0), queue_(max_size) {}

    bool push(int x) {
        if (size_ >= max_size_) {
            std::cout << "Queue is full" << std::endl;
            return false;
        }
        queue_[tail_] = x;
        tail_ = (tail_ + 1) % max_size_;
        ++size_;
        return true;
    }

    bool pop() {
        if (empty()) {
            std::cout << "Queue is empty" << std::endl;
            return false;
        }
        std::cout << queue_[head_] << std::endl;
        head_ = (head_ + 1) % max_size_;
        --size_;
        return true;
    }

    void peek() const {
        if (empty()) {
            std::cout << "Queue is empty" << std::endl;
        } else {
            std::cout << queue_[head_] << std::endl;
        }
    }

    void display_size() const {
        std::cout << size_ << std::endl;
    }

    bool empty() const {
        return size_ == 0;
    }

private:
    std::vector<int> queue_;
    int size_;
    int max_size_;
    int head_;
    int tail_;
};

int main() {
    std::ifstream fin("input.txt");
    if (!fin) {
        std::cerr << "Error opening file" << std::endl;
        return 1;
    }

    int count, size;
    fin >> count >> size;
    Queue queue(size);

    std::string command;
    int num;

    while (count-- > 0 && fin >> command) {
        if (command == "push") {
            fin >> num;
            queue.push(num);
        } else if (command == "pop") {
            queue.pop();
        } else if (command == "peek") {
            queue.peek();
        } else if (command == "size") {
            queue.display_size();
        }
    }

    return 0;
}

• BETTER POINT :

• Renamed the size() method to display_size() to avoid confusion with the size_ class member.
• Added checks to ensure the “input.txt” file opens correctly.
• Simplified the command reading loop using a while loop.
• Introduced the empty() method to check if the queue is empty before performing pop or peek.
• Provided more descriptive error messages for when the queue is full or empty.
• Made the peek() method const, as it does not modify the state of the object.
• Added boolean returns for the push and pop methods to indicate the success or failure of the operation.