push_back

Learn to add elements to a vector with push_back.

Adding elements with push_back

The common way to add an element to a vector is the push_back method. The call nums.push_back(10); appends the value to the end of the vector and increases the size by one. Creating an empty vector and calling push_back repeatedly is the quickest way to build a list that grows as you collect data.

The method name means 'push toward the back'; the element is always placed at the end. It does not insert in the middle; push_back only appends.

The size grows automatically

push_back increases the vector size by one on each call. On a three-element vector, calling nums.push_back(40); makes the size 4 and nums[3] now gives 40.

This automatic growth is the most important difference from C-style arrays. A C-style array has a size fixed at compile time; with std::vector the size changes at runtime. Memory management is automatic too; you just call push_back.

Exercise Add three elements with push_back

Declare an empty std::vector<int> nums;. Append the values 5, 10 and 15 in order with push_back. Then print size().

Show example solution

#include <iostream>
#include <vector>

int main() {
    std::vector<int> nums;
    nums.push_back(5);
    nums.push_back(10);
    nums.push_back(15);
    std::cout << nums.size() << std::endl;
    return 0;
}

Test yourself

Complete the push_back call
```
nums.____(10);
```
Show answer
```
nums.push_back(10);
```
After nums.push_back(40); what is the size? (nums started with 3)
```
std::vector<int> nums = {10, 20, 30};
nums.push_back(40);
```
- 4
- 3
- 30
- 40
Show answer

4 — the size goes from 3 to 4.
Match push_back behaviour

push_back

Appends an element
size()

Returns the count
nums[0]

Accesses first element
std::vector

Dynamic array container

Next lesson: size and at

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