Does It Matter If I Declare A Variable Inside A Loop?

Question

My question is that does it matter if I declare a variable outside the loop and reinitialize every time inside the loop or declaring and initializing inside the loop? So basically is there any difference between these two syntaxes (Performance,standard etc)?

Method 1

int a,count=0;
while(count<10)
   a=0;

Method 2

int count=0;
while(count<10)
   int a=0;

Please assume that this is only a part of a bigger program and that the body inside loop requires that the variable a have a value of 0 every time. So, will there be any difference in the execution times in both the methods?

Answer 1

Yes, it does matter. In second case

int count=0;
while(count<10)
   int a=0;

a can't be referenced out side of while loop. It has block scope; the portion of the program text in which the variable can be referenced.
Another thing that Jonathan Leffler pointed out in his answer is both of these loops are infinite loop. And second, the most important second snippet would not compile without {} (in C) because a variable definition/declaration is not a statement and cannot appear as the body of a loop.

 int count  =0;
 while(count++ < 10)
 {  
      int a=0;  
 }