What is an example of a do-while loop in C plus plus?

Answer 1

A do-while loop is best suited to loops that must execute at least once:

srand(( unsigned)time(NULL));

int i;

do {

// pick a random number between 1 and 10

i = 1 + (int) (10.0*(rand()/(RAND_MAX+1.0)));

std::cout << i << std::endl;

} while( i!=10 );

In this example, the loop executes at least once and prints a random number. While the random number is less than 10, the loop reiterates, selecting another random number until the number 10 is selected.

The exact same effect can be achieved with for and while loops but the code is much less readable as a result:

srand(( unsigned)time(NULL));

int i=0;

while( i!=10 )

{

// pick a random number between 1 and 10

i = 1 + (int) (10.0*(rand()/(RAND_MAX+1.0)));

std::cout << i << std::endl;

}

In the above example, we must initialise i before entering the loop for the first time.

srand(( unsigned)time(NULL));

for(;;)

{

// pick a random number between 1 and 10

int i = 1 + (int) (10.0*(rand()/(RAND_MAX+1.0)));

std::cout << i << std::endl;

if( i==10 )

break;

}

In the above example we use an infinite loop and instantiate i within the loop. We can also replace for(;;) with while(1) to achieve the same result.

Ultimately the do-while loop makes the most sense in this case. The infinite loop versions would only make sense if you wanted i to fall from scope at the end of the loop (which can't be done with a do-while loop since the conditional expression is outside of the loop). But the while loop makes the least sense because i must be initialised before entering the loop for the first time.