Difference between while loop and do while loop

Question

What is the difference between a while loop and a do while loop. I used to think both are completely same but then I came across following line of code:

do { printf("Word length... "); scanf("%d", &wdlen); } while(wdlen<2);

This code works perfectly and also prints word length and tascans the input but, once I changed it to

while(wdlen<2){ printf("Word length... "); scanf("%d", &wdlen); }

It gives a blank screen and fails to work. So there are some functional differences between both the loops. Can anybody explain this to me and also could I know if there is any difference between them?

Answer 1

The do while loop helps in executing the content of the loop once before checking the condition of the while. Wheras, a while loop will check the condition prior to executing the content. In this case you are waiting for a user input with scanf(), which will never execute in the while loop as wdlen which is not initialized and probably just contains a garbage value which could be greater than 2.