std::vector<int> numbers;

for (int i = 0; i < 100; ++i) {
    numbers.push_back(i);
}

std::vector<int> numbers;
numbers.reserve(100);

for (int i = 0; i < 100; ++i) {
    numbers.push_back(i);
}

std::vector<int> v;
v.reserve(100);

std::cout << v.size() << '\n';      // 0
std::cout << v.capacity() << '\n';  // 100

v.resize(100);

std::string text = "10 20 30 40";

#include <iostream>
#include <sstream>
#include <string>

std::istringstream input(text);

int value;

while (input >> value) {
    std::cout << value << '\n';
}

10
20
30
40

std::string point = "15 42";

std::istringstream input(point);

int x;
int y;

input >> x >> y;

if (!(input >> value)) {
    std::cout << "Invalid number\n";
}

Оставляю ссылочку: GitHub 📱

std::vector<int> numbers = {5, 1, 9, 3};

int max_value = numbers[0];

for (int value : numbers) {
    if (value > max_value) {
        max_value = value;
    }
}

auto max_it = std::max_element(
    numbers.begin(),
    numbers.end()
);

if (max_it != numbers.end()) {
    std::cout << *max_it << '\n';
}

9

auto best = std::max_element(
    users.begin(),
    users.end(),
    [](const User& a, const User& b) {
        return a.score < b.score;
    }
);

Оставляю ссылочку: GitHub 📱

std::vector<int> nums = {1, 2, 3, 4, 5};

nums.erase(
    std::remove_if(nums.begin(), nums.end(), [](int x) {
        return x % 2 == 0;
    }),
    nums.end()
);

std::erase_if(nums, [](int x) {
    return x % 2 == 0;
});

1 3 5

std::erase_if(users, [](const User& user) {
    return !user.active;
});

std::vector<int> v = {1, 2, 3};

for (int x : v) {
    v.push_back(x);
}

std::size_t n = v.size();

for (std::size_t i = 0; i < n; ++i) {
    v.push_back(v[i]);
}

v.reserve(v.size() * 2);