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    <p>This is a matter of style. My considerations:</p> <ol> <li><p>If the code block is small, in the end it won't matter where you place the declaration. However, it's preferable to have declarations <em>nearer</em> use, mainly in large code blocks. First, this way you can make sure that the variable wasn't modified until that point in the block, and second, because you can check the type and initialization of the variable faster.</p></li> <li><p>Besides, its faster to <em>code</em> by declaring variables near where you use them -- you don't have to scroll back to the beginning of the scope just to declared a forgotten variable and then move back.</p></li> <li><p>This isn't faster or slower. Variables, no matter where declared in the scope, will have their allocation and initialization centered at the beginning of the scope. This can be checked by generating IL for the language. </p></li> </ol> <p>For example, the code:</p> <pre><code>static void Main(string[] args) { var a = 3; if (a &gt; 1) { int b = 2; a += b; } var c = 10; Console.WriteLine(a + c); } </code></pre> <p>Generates the following IL:</p> <pre><code>.method private hidebysig static void Main(string[] args) cil managed { .entrypoint // Code size 24 (0x18) .maxstack 2 .locals init ([0] int32 a, // Declare a [1] int32 b, // Declare b [2] int32 c) // Declare c IL_0000: ldc.i4.3 IL_0001: stloc.0 IL_0002: ldloc.0 IL_0003: ldc.i4.1 IL_0004: ble.s IL_000c IL_0006: ldc.i4.2 IL_0007: stloc.1 IL_0008: ldloc.0 IL_0009: ldloc.1 IL_000a: add IL_000b: stloc.0 IL_000c: ldc.i4.s 10 IL_000e: stloc.2 IL_000f: ldloc.0 IL_0010: ldloc.2 IL_0011: add IL_0012: call void [mscorlib]System.Console::WriteLine(int32) IL_0017: ret } // end of method Program::Main </code></pre> <p>One important thing to notice is that variables in internal scopes, such as the variable b, which was at the if scope, is declared at method scope by the compiler.</p> <p>Hope it helps.</p>
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    1. COthanks, good explanation. So it seems to me that the memory is allocated by the way for all variables present in the function, either they may used or not. What makes diference, instead, is initialization of them. Thank you.!
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    2. COAfter analyzing an IL dump of the code, which is very similiar to your except that I use class and struct objects, the result is more or less the same. For first class citizen is allocated predefined space, for reference types pointer (4bytes), for value types (all of them even declared in the function's internal scope) allocated memory and intilaized (Doubt a little bit on intilization. Where actually the structure object declared in the function has become initialized ? Where we declare it, or were we first time use it ?
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    3. CO@Tigran: Local variables are never automatically initialized. The only time a local variable is assigned a value is when you explicitly do so. @Bruno: +1 for noting that no matter where variables are declared, storage from them is always allocated on loading the stack frame.
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