Thread: Getting the user to break a look

getchar doesn't work that way. Read about it: getchar

Your compiler should be yelling at you.


Quzah.

This:

Code:

    printf("Ready to go?  Y/N\n");
    scanf(yn)

is a compile error, but if you meant:

Code:

    scanf("%c", &yn);

There will be a '\n' left in the stdin buffer afterward, which may have consequences in the first iteration of your loop.

This:

Code:

    for (int y = 0; y < 10; y++)

would only be valid under c99. It's also problematic because you have redeclared an identifier (y).

This:

Code:

        getchar(a); // read a char from user
  
        // exit loop if user hits enter
        if (a == '\n')
            break;

Is not a legal getchar() call, and 'a' is not declared anywhere. In short your code is not compilable for a number of reasons, which would explain why you "cannot seem to get what [you] want". You need to start with some working code, eg:

Code:

#include <stdio.h>

int main() {
	printf("Ready to go?  Y/N\n");
	return 0;
}

And make sure it still compiles and runs when you add something new. Bonus point if it actually does what you want/expect.

Originally Posted by dwilliams

Yes the compiler is of course yelling at me

That's like "go to jail" in monopoly. Do not pass GO. Do not collect $200.

but I am having trouble understanding the concept of how the user can break the for loop.

It will not be possible for you to come to an understanding if you can't write compilable code. First, it has to run. Then you can try and make it run the way you want. Not the other way around. Otherwise you might as well just use:

Code:

break here if the user wants to;

Makes sense...but the compiler will yell Do not pass GO, do not collect...

Code:

Inside the loop I want the program to count to ten seconds then beep (\a). I want it to keep on doing this until the user presses a key.

I don't know how many consoles will actually beep, don't be surprised if it doesn't -- that's kind of an atavism. WRT to timing, you can do this with sleep(), but it is a non-standard function and its definition differs from implementation to implementation (eg, on linux the parameter is in seconds, on windows in milliseconds).

Originally Posted by MK27

would only be valid under c99. It's also problematic because you have redeclared an identifier (y).

That part is okay due to scope, but the global variable is redundant to begin with.

Edit:

I see that MK27 has already responded, so ignore this post. His contains much more relevant information.

Originally Posted by dwilliams

Yes the compiler is of course yelling at me but I am having trouble understanding the concept of how the user can break the for loop.

I don't have the answer, and haven't tried learning C programming in ages, but I noticed a few basic errors in your code:

• Missing semicolon after scanf(yn)
• Invalid use of getchar (as quzah mentioned)
• You're not checking the results of the input from the user whether they wish to start the loop
• Not an error per se, but GCC complained that I needed to use the --std=c99 option for the loop initial declaration
• You'll also want to handle converting the user's response to upper or lower case and compare appropriately to make sure they gave a valid response

I haven't looked up the syntax for scanf to fully understand it, but after looking up the info for getchar, I have the following code which still doesn't fully function, but may be closer to what you're looking for. At the very least I hope it illustrates the points I mentioned:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>

char yn;

int x, y;
int main()
{
    printf("Ready to go?  Y/N");
    yn = getchar();
    
    if ('Y' == toupper(yn))
    {
        
        printf("Press Enter or Return to Quit");
 
        // loop 500 times
        for (int y = 0; y < 10; y++)
        {
            printf("\a");
            yn = getchar(); // Toss first input as it was likely the
                            // Enter/Return key for getchar() input
            yn = getchar(); // read a char from user     
              
            // exit loop if user hits enter
            if (yn == '\n')
                break;
        }
    }
    
    return 0;
}

Here is a diff in case that makes it any easier to work with:

Code:

--- original-loop.c	2012-02-25 12:38:26 -0600
+++ loop.c	2012-02-25 12:36:41 -0600
@@ -1,22 +1,33 @@
 #include <stdio.h>
 #include <stdlib.h>
- 
+#include <ctype.h>
+
 char yn;
+
 int x, y;
 int main()
 {
-    printf("Ready to go?  Y/N\n");
-    scanf(yn)
-  
-    // loop 500 times
-    for (int y = 0; y < 10; y++)
+    printf("Ready to go?  Y/N");
+    yn = getchar();
+    
+    if ('Y' == toupper(yn))
     {
-        printf("\a")
-        getchar(a); // read a char from user
-  
-        // exit loop if user hits enter
-        if (a == '\n')
-            break;
+        
+        printf("Press Enter or Return to Quit");
+ 
+        // loop 500 times
+        for (int y = 0; y < 10; y++)
+        {
+            printf("\a");
+            yn = getchar(); // Toss first input as it was likely the
+                            // Enter/Return key for getchar() input
+            yn = getchar(); // read a char from user     
+              
+            // exit loop if user hits enter
+            if (yn == '\n')
+                break;
+        }
     }
-return 0;
+    
+    return 0;
 }

Again, this is still not functional, but hopefully it'll be useful in some way.