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How to Resolve Error "CS0029: Cannot implicitly convert type 'type' to 'type'" in C#

The Compiler Error CS0029 is a fundamental Type Mismatch error. The message states: "Cannot implicitly convert type 'TypeA' to 'TypeB'".

C# is a statically typed language, meaning variables are strictly defined by their data type. The compiler allows implicit conversions only when they are safe and no data loss can occur (e.g., converting an int to a long). If a conversion carries a risk of losing precision (like double to int) or if the types are fundamentally different (like string to int), the compiler refuses to do it automatically.

This guide explains how to handle these conversions manually using Casting, Parsing, or Conversion methods.

Understanding Implicit vs. Explicit Conversion​

  • Implicit (Automatic): Safe. int fits inside double. Child fits inside Parent.
  • Explicit (Manual): Potentially unsafe. double does not fit inside int (decimals are lost). Parent might not be Child.

CS0029 appears when you try to perform an explicit scenario using implicit syntax.

Scenario 1: Numeric Conversions (Possible Data Loss)​

You cannot assign a floating-point number (like double or float) to an integer variable because the decimal part would be truncated (lost). The compiler protects you from this accidental data loss.

Example of Mistake​

public void Calculate()
{
    double exactPrice = 19.99;
    
    // ⛔️ Error CS0029: Cannot implicitly convert type 'double' to 'int'
    int wholeNumberPrice = exactPrice; 
}

Solution: Explicit Cast​

If you are okay with losing the decimal precision, use a cast (int).

public void Calculate()
{
    double exactPrice = 19.99;
    
    // ✅ Correct: We explicitly tell the compiler "I know I will lose the .99"
    int wholeNumberPrice = (int)exactPrice; 
    
    System.Console.WriteLine(wholeNumberPrice); 
}
// Output: 19

Scenario 2: String to Other Types​

Strings are text. Even if the text is "100", it is not a number in memory. You cannot simply assign a string to an int or bool.

Example of Mistake​

public void ReadInput()
{
    string input = "50";
    
    // ⛔️ Error CS0029: Cannot implicitly convert type 'string' to 'int'
    int amount = input; 
}

Solution: Parsing​

You cannot "cast" a string (e.g., (int)input is also invalid). You must Parse or Convert it.

public void ReadInput()
{
    string input = "50";
    
    // ✅ Correct: Parse the string content into a number
    int amount = int.Parse(input);
    
    // Or use Convert
    int amount2 = System.Convert.ToInt32(input);
}
warning

int.Parse will throw an exception at runtime if the string does not contain a valid number (e.g., "Hello"). Use int.TryParse for safer code.

Scenario 3: Nullable Types to Non-Nullable​

A int? (Nullable Integer) can hold a number or null. A standard int can only hold a number. You cannot assign the nullable version to the standard version directly because if the value is null, the standard int would crash or be undefined.

Example of Mistake​

public void ProcessID(int? optionalId)
{
    // ⛔️ Error CS0029: Cannot implicitly convert type 'int?' to 'int'
    int safeId = optionalId;
}

Solution: Handle the Null​

You must decide what to do if the value is null. Typically, you use the null-coalescing operator (??) to provide a fallback.

public void ProcessID(int? optionalId)
{
    // ✅ Correct: Use 'optionalId', but if it is null, use 0 instead.
    int safeId = optionalId ?? 0;
    
    // Alternative:
    // int safeId = optionalId.GetValueOrDefault();
}

Scenario 4: Collections and Arrays​

In C#, a List<T> and an Array T[] are different types. You cannot assign one directly to the other.

Example of Mistake​

using System.Collections.Generic;

public void ProcessList()
{
    List<string> namesList = new List<string> { "Alice", "Bob" };
    
    // ⛔️ Error CS0029: Cannot implicitly convert type 'List<string>' to 'string[]'
    string[] namesArray = namesList;
}

Solution: Conversion Methods​

Use standard LINQ methods like .ToArray() or .ToList() to transform the collection.

using System.Collections.Generic;
using System.Linq; // Required for ToArray()

public void ProcessList()
{
    List<string> namesList = new List<string> { "Alice", "Bob" };
    
    // ✅ Correct: Create a new array from the list
    string[] namesArray = namesList.ToArray();
}

Conclusion​

CS0029 is the compiler telling you: "These shapes don't fit together automatically."

  1. Check Precision: If converting numbers, use a cast (int) if you accept data loss.
  2. Check Text: If converting strings, use .Parse() or Convert.
  3. Check Nulls: If converting nullable types, use ?? to provide a default value.
  4. Check Types: If converting collections, use .ToList() or .ToArray().

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