var a = 10;
const c = 15;

function print() {
  let b = 11;
  const d = 20;

  c = 18;   // here we got error for constant variable's value update or change
  console.log(a); // here a print as 10
  console.log(b); // here b print as 11
  console.log(c); // here c print as 15
  console.log(d); // here c print as 20
}

console.log(a); // here a print as 10
console.log(b) // here b print undefined
console.log(c) // here c print 15
console.log(d); // here d print as undefined