What is the different between while and do .... while in pension?

Answer 1

As an example for Daniel's nice explanation, compare these two blocks,

....

bool b1 = false;

while (b1) { // condition at first
cout << "Program flow skips this cout! ";
}

do {
cout << "This cout is going to execute at least once! ";
} while (b1); // condition at last

Answer 2

while first check condition and next run instructions

do while first run instructions and next check condition