Can anyone help me to clarify this doubt why j is not initialized in if block?

namespace consoleapplication3  {      class program      {          static void main(string[] args)          {              int = 10;              int j; // int j=10; got output 20 in console app if j declaring here , initializing -              if (a == 10)                                    //- in if block not getting output 20 why?              {                  j = 20;              }              console.writeline(j);
/*here not getting output instead of error coming use of unassigned local variable 'j' */
              console.readline();          }      }  }

while clear inspection j assigned value of 20 in if block, bit irrelevant error, couple of reasons.

the short answer c# language rules require j unconditionally assigned value before use it.  clearly in case j assigned value conditionally (the fact condition true not relevant language rules

another reason code flow analysis required determine j=20 line hit.  however code flow analysis done after code has been parsed , after cil has been generated, , long after uninitialized variable error has been generated.

finally, users find confusing changing line 

int = 10;

to

int = 9; 

would result in compile error 6 lines later.

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