Converting Recurision to Iteration - c

Question

How would I convert this code to use while loops instead of recursion?
void game(void)
{
int answer;
printf("%s", Questions[level]);
scanf("%d", &answer);
if (level < 8) {
if (is_right(level, answer)) {
printf("Good Job!\n");
level += 1;
game();
}
else {
printf("Sorry, you got the wrong answer. Try Again! \n");
sleep(1);
system("clear");
level = 0;
game();
}
}
else {
printf("Great Job, You Won!");
}
}
I tried starting with a while loop and trying to work backwards, but I got lost in the sea of code

Answer 1

There is a couple of "strange" things in your program that I'll get back to later but to start with let's focus on the question:
How would I convert this code to use while loops instead of recursion?
There are many ways to do that...
The current recursive calls, i.e. game();, takes no arguments, nor does it use a return value. So a very simple way to get rid of recursion and keeping the exact same functionality could be:
Add a while(1) loop around all the existing code
Replace the current recursive calls with a continue; statement
Add a break; statement when the loop is to terminate
That would look like:
void game(void)
{
while(1) { // Add a while loop
int answer;
printf("%s", Questions[level]);
scanf("%d", &answer);
if (level < 8) {
if (is_right(level, answer)) {
printf("Good Job!\n");
level += 1;
// game();
continue; // Start a new round of the game
}
else {
printf("Sorry, you got the wrong answer. Try Again! \n");
sleep(1);
system("clear");
level = 0;
//game();
continue; // Start a new round of the game
}
}
else {
printf("Great Job, You Won!");
break; // End the game by breaking out of the while loop
// This could also be a return; statement
}
}
}
The above solution preserves the structure of the original program. If we allow some (minor) restructuring, we can do a little better.
void game(void)
{
while(1) {
int answer;
printf("%s", Questions[level]);
scanf("%d", &answer);
// Check if the game has finished
if (level >= 8) {
printf("Great Job, You Won!");
return; // or break;
}
if (is_right(level, answer)) {
printf("Good Job!\n");
level += 1;
} else {
printf("Sorry, you got the wrong answer. Try Again! \n");
sleep(1);
system("clear");
level = 0;
}
}
}
Instead of checking for "shall game continue" the above version checks for "has game finished" and - if so - it returns. By doing that we no longer need the explicit continue; statements.
Now getting back to the "strange" things in your program:
When a user wins the game (i.e. level reach 8), the code will still ask one more question and once the answer has been entered, the program finish. That is probably not intended...
Further, the only way to finish the game is to win the game (i.e. answer correct a number of times in a row). I would expect a way for the user to say "I give up"
Finally there is a serious problem with your code that may lead to errors like program crash or infinite loop. Always, always, always, check the return value of scanf !!! (see end-note)
Fixing those things and doing a little more restructuring could lead to a program like:
void game(void)
{
level = 0; // Assuming a new game always starts a level zero
while(1) {
int answer;
printf("%s", Questions[level]);
if (scanf("%d", &answer) != 1) {
// Wrong input or input error
// Add error handling... but for now, just terminate
exit(1);
}
// Let the user end the program with a negative input
if (answer < 0) {
printf("Sorry to see you leave before finishing the game. Bye.\n");
return 0;
}
if (is_right(level, answer)) {
printf("Good Job!\n");
level += 1;
// Check if the game has finished
if (level == 8) {
printf("Great Job, You Won!");
return;
}
} else {
printf("Sorry, you got the wrong answer. Try Again! \n");
sleep(1);
system("clear");
level = 0;
}
}
}
End-note:
While it's true that the return value from scanf shall be checked, the better advice would be:
Never use scanf.
At the surface scanf looks like an easy way to get user input but the truth is that it has so many pitfalls that only real experts are able to use it (and they probably wont). The number of SO questions where (incorrect use of) scanf is the root cause of a problem is extreme. And they keep coming...
So forget that you ever heard about scanf. If you do like the features of scanf, you will (nearly) always do better by using fgets followed by sscanf.

Answer 2

It is hard to call it recursion.
void game(void)
{
int answer;
while (level < 8)
{
printf("%s", Questions[level]);
if(scanf("%d", &answer) != 1){ /* handle error */}
if (is_right(level, answer))
{
printf("Good Job!\n");
level += 1;
}
else
{
printf("Sorry, you got the wrong answer. Try Again! \n");
sleep(1);
system("clear");
level = 0;
}
}
printf("Great Job, You Won!");
}