---
title: 1.12 Type Deduction (auto)
description: "The `auto` keyword allows the compiler to determine the data type of a variable from its initializer. This reduces the need to specify the type explicitly and helps simplify declarations. This example demonstrates how `auto` deduces the type of different…"
url: "https://edcret.in/docs/cpp-programming/basic-refreshers-cplusplus/1-12-type-deduction-auto/"
updated: "2026-07-28"
category: C++ Programming / Basic Refreshers
---

# 1.12 Type Deduction (auto)

The `auto` keyword allows the compiler to determine the data type of a variable from its initializer. This reduces the need to specify the type explicitly and helps simplify declarations.

This example demonstrates how `auto` deduces the type of different variables during compilation.

## Source Code

```
#include <iostream>

int main()
{
    auto age = 21;
    auto salary = 55000.75;
    auto grade = 'A';

    std::cout << "Age: " << age << '\n';
    std::cout << "Salary: " << salary << '\n';
    std::cout << "Grade: " << grade << '\n';

    return 0;
}
```

## Output

```
Age: 21
Salary: 55000.8
Grade: A
```

## Explanation

- `auto age = 21;` declares `age` and deduces its type as `int` because the initializer is an integer literal.
- `auto salary = 55000.75;` deduces the type as `double` since floating-point literals are of type `double` by default.
- `auto grade = 'A';` deduces the type as `char` because the initializer is a character literal.
- The type deduction performed by `auto` occurs during compilation. After deduction, the variable has a fixed type and behaves like any other variable of that type.
- An `auto` variable must be initialized when it is declared because the compiler requires the initializer to determine its type.
- `std::cout` prints the values stored in the variables without requiring knowledge of their explicitly written types.
- `return 0;` terminates the program successfully.