Question

Im new to C# and I am having difficulty understanding Do while loops. My project asks for one functions that reads a word, and gives a number placement for a letter. How would a use a do while loop for this (my teacher said this would be easiest however i can use other methods)

static void WordAnalyzer()
{
string word;
char letter;
do
{
Console.WriteLine("Given a word I will be able to let you know what letters are used; and their order number in the word:");
while (letter != 1);
{

Answer 1

I'm not really a C guy, but I'll show an example of how I can practically implement do while loops to help your understanding.

First I'll explain it a little. In a traditional while loop, you *first* check the boolean expression before executing the code block:
```
while(theChefCooks) {
i_eat();
chefThinksIfHeWantsToKeepCooking();
}
```
Then after the code block executes, it will test the boolean expression again, and if it's true, it repeats.

However, in a do-while loop, it will *always* execute the code block once before testing the boolean expression, and before it decides it wants to loop.

I typically use do-while loops when doing input validation, here's one cheesy but practical example asking the user to input the year they were born.
```
boolean is4Characters = false;
boolean isANumber = false;
boolean isWithin120Years = false;

do{
String input = askUserTheirBirthYear();

String message = "";
if(input.length() != 4) {
is4Characters = false;
message = "Your input was not 4 characters long. ";
}
else {
is4Characters = true;
}

if(!isValidNumber(input)) {
isANumber = false;
message += "Your input was not a valid number. ";
}
else {
isANumber = true;
}

if(!isANumberWithinLast120Years(input)) {
isWithin120Years = false;
if(isANumber && is4Characters) {
message += "Your input was not a number within the last 120 years.";
}
}
else {
isWithin120Years = true;
}

if(isANumber && is4Characters && isWithin120Years) {
message = "valid input.";
}

printMessageToUser(message);
}while(!is4Characters || !isANumber || !isWithin120Years);


```

Answer 2

do/while loops mirror while/do loops. The differences are that because the condition is tested at the end, the code in a while/do loop will execute at least once. A do/while loop won't execute if it's condition is never true. When I read files byte by byte in C, I use a do/while loop and test for end of file after each byte is read.

Answer 3

BTW, the code in your question will probably work if you move the while statement after the '}'.