Question

What is the difference between:

if      (expr1) {stmt}
else if (expr2) {stmt}
else if (expr3) {stmt}    
else            {stmt}

And the same code block written as:

if (expr1) {stmt}
if (expr2) {stmt}
if (expr3) {stmt}    
else       {stmt}

Answer 1

In the first one, each block of statements is mutually exclusive; the structure guarantees that exactly one of them will get executed.

This is not true for the second one. Consider:

if (a == 2) { /* blah */ }
if (a == 3) { /* blah */ }
if (a < 5)  { /* blah */ }

If a == 2, then two of the blocks will get executed.