Summary - std::vector

Combine push_back, size and range-based for to write a class list.

Summary: std::vector

In this group you learned std::vector: the dynamic-size array container. It starts with #include <vector>, is declared as std::vector<int> nums; and grows with push_back.

You saw three core access paths: size() counts, at(i) accesses with bounds checking, and [] accesses fast but unchecked. Finally you walked through all elements with a range-based for. These are the foundations of working with list-shaped data in C++.

Exercise Sum grades with range-for

Declare std::vector<int> grades = {85, 90, 78};. Sum the grades with a range-based for, then print the average (integer division) using std::cout.

Show example solution

#include <iostream>
#include <vector>

int main() {
    std::vector<int> grades = {85, 90, 78};
    int sum = 0;
    for (int g : grades) {
        sum += g;
    }
    std::cout << sum / grades.size() << std::endl;
    return 0;
}

Exercise Build the vector and print the last element

Declare an empty std::vector<int> v. Append the values 7, 14 and 21 with push_back. Then print size() and the last element v.at(v.size()-1).

Show example solution

#include <iostream>
#include <vector>

int main() {
    std::vector<int> v;
    v.push_back(7);
    v.push_back(14);
    v.push_back(21);
    std::cout << v.size() << " " << v.at(v.size() - 1) << std::endl;
    return 0;
}

Test yourself

Match the concepts

push_back

Appends
size()

Counts
at(i)

Checked access
for (int x : v)

Iterates
Which method checks bounds?
```
nums.???(i)
```
- nums.at(i)
- nums.push_back(i)
- nums[i]
- nums.size()
Show answer

nums.at(i) — at(i) checks bounds and throws on an invalid index.
Append with push_back
```
v.____(42);
```
Show answer
```
v.push_back(42);
```

Next lesson: Defining functions

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