Why the output is different when we add 'int' tag twice in a program when using 'for' loop?

Question

I am a learner and new to C language. While I was creating a function which will give power of two numbers using for loop I encounter that using int declaration before loop

Answer 1

Because the 'scope' of r in the second code is inside the loop, when you leave the loop the variable is not longer valid.

  for (k = 1; k <= y; k++)
  {
       int r = r * x; //here you create the variable
  } //here it is destroyed

In c/c++ the variables are local to a scope, when you leave the scope you loose the variable. Everything inside {} is a scope (internal to the outside scope). Inside scopes can see variables of outside scope.

void func()
{ // begin scope of a function

   // can't see any variables defined inside the scope of the while
   // they don't exists yet
   while ()
   { // begin scope of a while
     // can see variables defined inside the scope of the function
   }

   // can't see any variables defined inside the scope of the while
   // they don't exists anymore
}