---
title: 6.9 Passing by Value
description: "Passing by value means that a function receives a copy of the argument supplied by the caller. Changes made to the parameter inside the function do not affect the original variable. This is the default parameter-passing mechanism for ordinary non-reference…"
url: "https://edcret.in/docs/cpp-programming/functions/6-9-passing-by-value/"
updated: "2026-09-06"
category: C++ Programming / Functions
---

# 6.9 Passing by Value

Passing by value means that a function receives a copy of the argument supplied by the caller. Changes made to the parameter inside the function do not affect the original variable.

This is the default parameter-passing mechanism for ordinary non-reference parameters in C++. It provides isolation between the function's local parameter and the caller's original object.

## Source Code

```
#include <iostream>

void updateValue(int value)
{
    value = 100;

    std::cout << "Inside Function: " << value << '\n';
}

int main()
{
    int number = 50;

    updateValue(number);

    std::cout << "Outside Function: " << number << '\n';

    return 0;
}
```

## Output

```
Inside Function: 100
Outside Function: 50
```

## Explanation

- `updateValue(int value)` defines a function with an `int` parameter named `value`.
- `updateValue(number)` passes the value stored in `number` to the function.
- Because `value` is passed by value, the function receives a copy of `number`.
- `value = 100;` modifies only the local copy inside the function.
- The original `number` variable remains unchanged.
- The value displayed inside the function is therefore `100`.
- After the function returns, `number` still contains its original value, `50`.
- Passing by value is useful when a function should work with a value without modifying the caller's original variable.
- `return 0;` terminates the program successfully.