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# 04. Typedef

`typedef` lets you give an **alias** (a new, custom name) to an existing type. It doesn't create a new type, it's just a nickname that makes code easier to read and write.

```cpp
#include <iostream>

typedef std::string text_t;

int main() {
    text_t firstName = "Bro";

    std::cout << firstName << '\n';

    return 0;
}
```

Here `text_t` is just another name for `std::string`. `text_t firstName = "Bro";` behaves exactly like `std::string firstName = "Bro";`.

**Syntax:** `typedef ExistingType NewName;`

***

### Why use `typedef`?

* **Shorter, clearer names** — especially for long or ugly types (looking at you, `std::vector<std::pair<std::string, int>>`).
* **Easier to change later** — update the type in one place instead of everywhere it's used.
* **Self-documenting code** — `text_t` or `age_t` tells you what the value *represents*, not just its raw type.

```cpp
// without typedef — long and easy to typo
std::vector<std::pair<std::string, int>> scores;

// with typedef — short and clear
typedef std::vector<std::pair<std::string, int>> scoreList_t;
scoreList_t scores;
```

***

### More cool examples

#### 1. Aliasing numeric types

```cpp
#include <iostream>

typedef unsigned long ulong_t;
typedef double money_t;

int main() {
    ulong_t population = 8000000000;
    money_t price = 19.99;

    std::cout << "Population: " << population << '\n';
    std::cout << "Price: $" << price << '\n';

    return 0;
}
```

#### 2. Aliasing a `std::vector`

```cpp
#include <iostream>
#include <vector>

typedef std::vector<int> intList_t;

int main() {
    intList_t scores = {90, 85, 77, 100};

    for (int score : scores) {
        std::cout << score << ' ';
    }
    std::cout << '\n';

    return 0;
}
```

#### 3. Aliasing a `std::pair` (name + age)

```cpp
#include <iostream>
#include <utility>
#include <string>

typedef std::pair<std::string, int> person_t;

int main() {
    person_t p1 = {"Ronaldo", 39};

    std::cout << p1.first << " is " << p1.second << " years old\n";

    return 0;
}
```

#### 4. The commented-out example from your screenshot, explained

```cpp
#include <vector>
#include <string>
#include <utility>

// A list of (name, id) pairs
typedef std::vector<std::pair<std::string, int>> nameIdList_t;

int main() {
    nameIdList_t users = {
        {"Alice", 1},
        {"Bob", 2}
    };

    for (auto& user : users) {
        std::cout << user.first << " -> ID " << user.second << '\n';
    }

    return 0;
}
```

Without `typedef`, you'd have to write `std::vector<std::pair<std::string, int>>` **every single time** you declare something of this type. One alias, used everywhere.

#### 5. `typedef` for function pointers (more advanced, good to recognize)

```cpp
#include <iostream>

typedef int (*operation_t)(int, int);

int add(int a, int b) { return a + b; }
int multiply(int a, int b) { return a * b; }

int main() {
    operation_t op = add;
    std::cout << "Add: " << op(3, 4) << '\n';

    op = multiply;
    std::cout << "Multiply: " << op(3, 4) << '\n';

    return 0;
}
```

***

### `typedef` vs `using` (modern alternative)

Since C++11, `using` can do the same job — and most modern code prefers it because it reads left-to-right and handles templates more cleanly.

```cpp
typedef std::string text_t;   // old style
using text_t = std::string;   // modern style, same result
```

```cpp
typedef std::vector<int> intList_t;   // old style
using intList_t = std::vector<int>;   // modern style
```

Both work. `typedef` is older (from C) and still very common in existing codebases; `using` is the recommended style for new code.

***

### Quick Recap

* `typedef ExistingType NewName;` creates an alias, not a new type.
* Great for shortening long/complex types like `std::vector<std::pair<...>>`.
* Makes code more readable and easier to maintain.
* Modern C++ (11+) prefers `using NewName = ExistingType;` for the same purpose.


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