Q.Explain the difference between a while loop and a do...while loop. Write a while loop that prints the numbers 1 to 5.

Both repeat a block, but they differ in when the condition is checked, which affects the minimum number of runs. …

while — entry-controlled. The condition is checked before the body runs. If it is false at the very start, the body is skipped entirely, so a while loop can run zero times:

int i = 1;
while (i <= 5) {
    System.out.println(i);   // prints 1, 2, 3, 4, 5
    i++;                     // update — moves toward ending the loop
}

do...while — exit-controlled. The body runs first, and the condition is checked afterwards. So the body always runs at least once, even if the condition is false:

int n = 1;
do {
    System.out.println(n);
    n++;
} while (n <= 5);

The key difference is when the test happens:

The same output can be produced by a for loop: `for (int i = 1; i <= …

Forgetting the update (i++), which makes the condition never become false — an infinite loop. Also placing a semicolon right after while (i <= 5) …