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How to Resolve Error "CS0819: Implicitly-typed variables cannot have multiple declarators" in C#

The Compiler Error CS0819 is a syntax restriction error regarding the var keyword. The message reads: "Implicitly-typed variables cannot have multiple declarators".

In C#, you are allowed to declare multiple variables of the same explicit type in a single statement using commas (e.g., int a = 1, b = 2;). However, the var keyword (Implicit Typing) does not support this syntax. When you use var, the compiler infers the type from the expression on the right. To keep type inference logic deterministic and readable, C# enforces a rule: One var declaration per statement.

This guide explains the restriction and provides standard workarounds.

Understanding Multiple Declarators​

A "Declarator" is the part of the statement that names the variable and assigns it a value.

  • Explicit Type: int x = 10, y = 20;
    • Here, int applies to both x and y. This is valid.
  • Implicit Type: var x = 10, y = 20;
    • Here, the compiler rejects the syntax. Even though both are integers, var cannot be distributed across multiple variables in one line.

Scenario 1: Comma-Separated Declarations​

This is the most direct cause. You try to shorten your code by declaring two variables on one line using var.

Example of error​

public void Setup()
{
    // ⛔️ Error CS0819: Implicitly-typed variables cannot have multiple declarators.
    var a = 10, b = 20; 
    
    // Also invalid even if types differ (which would be invalid explicitly anyway)
    // var s = "Hello", i = 50; 
}

Solution 1: Use Separate Statements​

The cleanest fix is to declare each variable on its own line using var.

public void Setup()
{
    // ✅ Correct: Each 'var' infers its own type independently.
    var a = 10;
    var b = 20;
}

Solution 2: Use Explicit Typing​

If you really want them on the same line, and they are the same type, simply replace var with the concrete type.

public void Setup()
{
    // ✅ Correct: Standard C# syntax for multiple declarators.
    int a = 10, b = 20;
}

Scenario 2: The for Loop Limitation​

This error frequently catches developers when writing for loops. It is common to initialize two index variables (e.g., one moving forward, one moving backward) in the loop header.

Example of error​

Attempting to use var for multiple loop variables.

public void ReverseArray(int[] arr)
{
    // ⛔️ Error CS0819: You cannot use 'var' for both i and j here.
    for (var i = 0, j = arr.Length - 1; i < j; i++, j--)
    {
        // Swap logic...
    }
}

Solution 1: Use Explicit Types​

Since loop counters are almost always integers, explicit typing is the best fix here.

public void ReverseArray(int[] arr)
{
    // ✅ Correct: Using 'int' allows multiple declarators.
    for (int i = 0, j = arr.Length - 1; i < j; i++, j--)
    {
        var temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
    }
}

Solution 2: Separate the Declarations​

If the types are complex and you really want to use var (or if the types are different), declare the variables before the loop.

public void ReverseArray(int[] arr)
{
    // ✅ Correct: Variables declared outside.
    var i = 0;
    var j = arr.Length - 1;

    // The initialization section of the loop is now empty.
    for (; i < j; i++, j--)
    {
        // Swap logic...
    }
}
note

If the variables have different types (e.g., int i and double d), you must use Solution 2 (declare outside) because a for loop header only supports a single type declaration.

Conclusion​

CS0819 enforces simplicity in type inference.

  1. One Line, One Var: Treat var as a 1-to-1 mapping. One variable per var keyword.
  2. Explicit for Multiples: If you want comma-separated lists (a=1, b=2), you must use the explicit type name (int).
  3. For Loops: Use int instead of var if you need multiple loop counters.

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