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do statement while (condition); |
Its functionality is exactly the same as the while loop except that condition in the do-while is evaluated after the execution of statement instead of before, granting at least one execution of statement even if condition is never fulfilled. For example, the following program echoes any number you enter until you enter 0.
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// number echoer #include <iostream.h> int main () { unsigned long n; do { cout << "Enter number (0 to end): "; cin >> n; cout << "You entered: " << n << "\n"; } while (n != 0); return 0; } |
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#include <iostream> using namespace std; int main () { // Local variable declaration: int a = 10; // do loop execution do { cout << "value of a: " << a << endl; a = a + 1; } while( a < 20 ); return 0; } |
The do-while loop is usually used when the condition that has to determine its end is determined within the loop statement, like in the previous case, where the user input within the block of intructions is what determines the end of the loop. If you never enter the 0 value in the previous example the loop will never end.
