very basic program just exits

[seal]

This is the same code from the tutorial, and i was reading it, but once i execute it, it just quits when i enter an age and press enter... why is that?

#include <stdio.h>

int main ()

{
    int age;
    printf ("please enter your age");
    scanf ( "%d", &age );
    if ( age < 40 ) 
    {
     printf ("You are not old enough!\n");
}
 else if (age == 40 )
{
      printf ("You are borderline!\n");
}
 else
{
printf ("You're pushing it buddy!");
}
 return 0;
}

[Salem]

http://faq.cprogramming.com/cgi-bin/...&id=1043284385

[seal]

cool thx

but how would i make it so that after it tells me if i'm not old enough or w/e that it waits for me to press enter and doesnt just quit on its own?

i put getchar () at the end but that didnt do anything

oh and what is the \n that was put in the tutorial? if i take it out, it makes no diffrence

[kermit]

I would imagine that the newline which the earlier call to scanf() did not read in (the newline which you entered by pressing <ENTER> after the number you entered) is still sitting in the buffer, and when the program gets to the getchar(), there is a newline there waiting for it, so it does not need you to press <ENTER> again.

Try something like this:

#include <stdio.h>

int main()
{
        int c;
        int age;
        printf("please enter your age");
        scanf("%d", &age);
        while ((c = getchar()) != EOF && c != '\n') {
                ;
        }
        if (age < 40) {
                printf("You are not old enough!\n");
        } else if (age == 40) {
                printf("You are borderline!\n");
        } else {
                printf("You're pushing it buddy!");
        }
        getchar();
        return 0;
}

This code

 while ((c = getchar()) != EOF && c != '\n') {
                ;
        }

makes repeated calls to getchar() as long as the condition is not EOF or a '\n' (newline) - it basically 'eats' every remaining character (including the newline) in the buffer. The ; on the line all by itself is a nulll statement - all of the actual work is done in the while statment one line above, but syntactically, the semicolon ';' is necessary so we add it - it could have been placed right after the while statement on the same line like so:

while ((c = getchar()) != EOF && c != '\n') ;

But I prefer to have it out on its own line so there is no mistaking that it is indeed a null statement - but each to his own on style issues like that one.

As to the '\n', that is your newline (as I mentioned above) - it is the way that you represent a character that does not really have a representation - similar characters would be '\t' for a tab, and '\b' for a backspace. A ' ' would be a space obviously.

[quzah]

The ; on the line all by itself is a nulll statement - all of the actual work is done in the while statment one line above, but syntactically, the semicolon ';' is necessary so we add it - it could have been placed right after the while statement on the same line like so:

while ((c = getchar()) != EOF && c != '\n') ;

But I prefer to have it out on its own line so there is no mistaking that it is indeed a null statement - but each to his own on style issues like that one.

while( (c=getchar()) != EOF && c != '\n' ){ }

Quzah.

[seal]

man this stuff is confusing...

programming is something that i've always wanted to do, but they just all seem so confusing...

[seal]

where exactly do i need these ?

{ and }

i thought it was like where your 'program' sits in... one in the beginning, and one in the end.... but apparently not lol

[quzah]

They define the beginning and end of a block (new scope) of code. They're also used for initializing arrays, and in the definition of structures. Here however, I'm just using them in place of a single ; operator, just to show that you don't really have to have the ;. I'm defining an empty block of code. It doesn't do anything at all. However, in this case it acts like an empty statement (the ; by itself).

There's a decent number of us around here who like to be pedantic about things, so when someone says something like "never" or "always", and the like, we like to point out things which don't fit the statement.


Quzah.

[ZuK]

while ((c = getchar()) != EOF && c != '\n') ;

is just the same as

while ((c = getchar()) != EOF && c != '\n') {}

It just means while getchar does not return end of file and getchar returns new line do nothing => remove new lines from the buffer.
Kurt

[seal]

ahhh i see....

shouldnt it be

{
 while ((c = getchar()) != EOF && c != '\n') 
}

?

also what is %d ?

sorry for such basic questions guys, this is how i learn, i ask and i finally get it...

about 4 years ago i didnt know what an alternator on a car was for...
now i have rebuilt motors from the block scratch using message boards' helps

[ZuK]

{
 while ((c = getchar()) != EOF && c != '\n') 
}

This would give you a syntax error. ( missing semicolon )
Kurt

[Lionmane]

That goes back to what quzah said:

They define the beginning and end of a block (new scope) of code.

The way you used the curly brackets means that the code inside will be executed unconditionally (ie: you won't see a difference).

The curly brackets tells the computer "execute this code seperately from normal", and you have to define a condition above it so that it only executes when your condition is met.

mw

[quzah]

It just means while getchar does not return end of file and getchar returns new line do nothing => remove new lines from the buffer.
Kurt

Actually, it removes everything from the buffer, one character at a time. It only stops on EOF or a newline.

That goes back to what quzah said:

The way you used the curly brackets means that the code inside will be executed unconditionally (ie: you won't see a difference).

The curly brackets tells the computer "execute this code seperately from normal", and you have to define a condition above it so that it only executes when your condition is met.

mw

To further the point, you can use { } nearly any time you like. For example, you could do this:

int main ( void )
{
    {
        {
        }
    }
    {
        {
        }
    }
    {
        {
        }
    }
    return 0;
}

Now it doesn't do much of anything here, but it's fine to do so. One thing to note when defining new code blocks (scope blocks) is that you can define new variables at the beginning of scope. These variables end with the end of scope (there's a way around that, but ignore it for now). So, you could do this:

int main ( void )
{
    int x;
    {
        int y; /*x and y are here */
        {
            int z; /* x, y, z are here */
        }
        /* z is gone */
    }
    /* y and z are gone */
    {
        int y; /* x and a different y are here */
        {
            int z; /* x and a the new y are here, along with a new z */
        }
        /* the new z is gone... */
    }
    /* and so on... */
    {
        int y;
        {
            int z;
        }
    }
    return 0;
}

Quzah.

[Thantos]

To make things even more confusing you can even declare a new variable with the same name.

int main()
{
  int x=3;
  {
    int x=5;
    printf("%d\n", x);  /* Prints 5 */
  }
  printf("%d\n", x); /* Prints 3 */
  return 0;
}

Oh the fun

[dwks]

No, it doesn't. You need <stdio.h>.