5.18.txt

a)
do
	int v1, v2;
	cout << "Please enter two numbers to sum:" ;
	if (cin >> v1 >> v2)
		cout << "Sum is: " << v1 + v2 << endl;
while (cin);

// this do-while loop is incorrect, because it doesn't have curly braces in it to form a block for the multiple statements

fix:

do {
	int v1, v2;
	cout << "Please enter two numbers to sum:";
	if (cin >> v1 >> v2)
		cout << "Sum is: " << v1 + v2 << endl;
} while (cin);

// this loop prompts the user for two numbers, adds them up and prints their sum, loops until the user enters an invalid input

b)
do {
	//	...
} while (int ival = get_response());

// this loop is invalid because you can't have a variable definition inside the while's condition in a do-while loop

fix:

int ival;
do {
	//	...
} while (ival = get_response());

// now this loop loops until ival gets a false value (zero in case of an int)

c)
do {
	int ival = get_response();
} while (ival);

// error: the variable in the condition of a do-while loop needs to be declared outside of the statement body

fix:

int ival;
do {
	ival = get_response();
} while (ival);