do while

The do while loop allows to repeat a statement as long as a certain expression’s value is or converts to true. The statement is executed at least once. For example, the loop reported in the program below reads grades from the user and sums them into gradeSum. The loop body executes at least once, and the loop iterates until a grade equal to 0 is input. In case the body is a single statement, and not a block, parentheses, just like for other loops, are unnecessary: 
do cout << i++ << endl; // no parenthesis with one statement
while(i <= 10);


Example


#include <iostream>
using namespace std;

int main()
{   
    int grade;
    double gradeSum = 0;
    int gradeCount = 0;
    do // sums grades input
    {
        cout << "Enter a grade (0 to quit): ";
        cin >> grade;
        gradeSum += grade;
        gradeCount++;
    }
    while(grade);

    cout << "The grade average is: " << (gradeSum ? gradeSum/--gradeCount : 0) << endl << endl;  

    int i = 1;
    do cout << i++ << endl; // no parentheses with one statement
    while(i <= 10);
}

Output

Enter a grade (0 to quit): 5
Enter a grade (0 to quit): 2
Enter a grade (0 to quit): 7
Enter a grade (0 to quit): 0
The grade average is: 4.66667

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