---
title: 3.21 Comma Operator (,)
description: "The comma operator (`,`) evaluates two or more expressions from left to right and returns the value of the last expression. Each expression is evaluated completely before the next expression is evaluated. Although the comma operator can combine multiple expressions…"
url: "https://edcret.in/docs/cpp-programming/operators-cplusplus/3-21-comma-operator/"
updated: "2026-07-28"
category: C++ Programming / Operators
---

# 3.21 Comma Operator (,)

The comma operator (`,`) evaluates two or more expressions from left to right and returns the value of the last expression. Each expression is evaluated completely before the next expression is evaluated.

Although the comma operator can combine multiple expressions into a single statement, it is used less frequently in modern C++ because separate statements are generally easier to read. It is still commonly encountered in `for` loops and certain compact expressions.

## Source Code

```
#include <iostream>

int main()
{
    int a = 10;
    int b = 20;

    int result = (a += 5, b += 10, a + b);

    std::cout << "Value of a : " << a << '\n';
    std::cout << "Value of b : " << b << '\n';
    std::cout << "Result     : " << result << '\n';

    return 0;
}
```

## Output

```
Value of a : 15
Value of b : 30
Result     : 45
```

## Explanation

- The comma operator (`,`) evaluates multiple expressions from left to right.
- Each expression is evaluated completely before the next expression begins.
- `a += 5` updates the value of `a` from `10` to `15`.
- `b += 10` updates the value of `b` from `20` to `30`.
- The final expression `a + b` evaluates to `45`.
- The value of the last expression becomes the result of the entire comma expression and is assigned to `result`.
- The comma operator is commonly used in `for` loop expressions and other situations where multiple operations are required in a single expression.
- `return 0;` terminates the program successfully.