Why Does One C# Code Sample Compile While the Other Fails Due to Variable Scope?

Detailed explanation of C# variable scope: Why does one code example compile and pass, but the other fails due to variable scope?

The following explains the C# variable scoping rules that cause the compilation results of these two code examples to be different.

Code example 1: Compilation failed

In the first code example, the first declaration of variable i (int i=10; // Point1) within the for loop causes a compilation error. This is because the variable i has been declared in the method containing the loop. The C# specification stipulates that multiple elements with the same name are not allowed to exist within the local variable declaration space.

In addition, the second reference to objX outside the for loop (var objX = new OtherClassOfMine(); // Point2) also causes a compilation error. This is because the variable objX has been declared inside the for loop and according to the C# specification, a simple name such as objX used in a nested block must refer to the same entity within the block.

Code example 2: Compilation successful

In the second code example, the two for loops declare the variables i and objX within their respective blocks. Since each block uses its own set of variable declarations, there is no overlap in variable names or scopes and the code compiles successfully.

Summary:

Code example 1 violates the variable declaration space rules and declares multiple variables with the same name in the same scope. Code Example 2 avoids this problem by declaring the variables in separate blocks. Understanding these scoping rules is crucial to writing correct and maintainable C# code.

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