scanf() problem

[suzanna]

I'm just starting C language classes, and I have searched around to understand why that part of my code behaves the way it does and come to find this site, a page titled "Warning against Scanf" where it says scanf() is less prone to errors when it's used along with fgets().

Now, we haven't studied fgets() yet and I don't know the correct syntax for it. This is the part of my code that causes a problem.

=============== =============== =============

/*asks a user to enter a number less than 25 and gives a warning if a number greater than 25 is entered*/

int x=26;

printf("enter a number");

while(x>25)
{
scanf("%d",&x);

if(x>25)
printf("Enter a number less or equal to 25");
else
printf("the number you entered is %d",x);
}
=============== =============== =============== =

Now this segment works fine as long as the user enters a number, but it starts acting weird if a character or an array of characters is entered.

how do I use fget() in this case? and is there a way to handle this issue without using fget()? like tweaking scanf() or something?

[JosAH]

I'm just starting C language classes, and I have searched around to understand why that part of my code behaves the way it does and come to find this site, a page titled "Warning against Scanf" where it says scanf() is less prone to errors when it's used along with fgets().

Now, we haven't studied fgets() yet and I don't know the correct syntax for it. This is the part of my code that causes a problem.

=============== =============== =============

/*asks a user to enter a number less than 25 and gives a warning if a number greater than 25 is entered*/

int x=26;

printf("enter a number");

while(x>25)
{
scanf("%d",&x);

if(x>25)
printf("Enter a number less or equal to 25");
else
printf("the number you entered is %d",x);
}
=============== =============== =============== =

Now this segment works fine as long as the user enters a number, but it starts acting weird if a character or an array of characters is entered.

how do I use fget() in this case? and is there a way to handle this issue without using fget()? like tweaking scanf() or something?

You're not supposed to tweak anything that is part of the Standard ;-) Note that
scanf() returns the number of actually scanned items. So if the user types anything
else but a number scanf() will return 0 (zero) given your "%d" scan format string.
Your program should handle that situation.

kind regards,

Jos

[suzanna]

You're not supposed to tweak anything that is part of the Standard ;-) Note that
scanf() returns the number of actually scanned items. So if the user types anything
else but a number scanf() will return 0 (zero) given your "%d" scan format string.
Your program should handle that situation.

kind regards,

Jos

When I try and enter a character, it goes into an infinite loop. Why does that happen?

[JosAH]

When I try and enter a character, it goes into an infinite loop. Why does that happen?

As I wrote: scanf() doesn't 'eat' the faulty character. Suppose I enter "a123" and
scanf should scan a "%d" (i.e. an integer number); it 'sees' the 'a' and simply
bails out, leaving that 'a' in the input stream. Then you try again: same result;
and again and again.

According to the scanf() return value you should discard that offending character
or even the entire line or whatever suits you fine. Simply retrying things again
and again in a loop doesn't work: i.e. scanf() would reject that same character
again and again.

kind regards,

Jos

[suzanna]

and an fgets() would flush out the garbage character? so what is the correct syntax?

[weaknessforcats]

Use getch() to eat the offending byte. fgets() is for extracting an entire C string from the input buffer.

[suzanna]

This is out of my current knowledge, i'm tied to the total basics. maybe you could show me an example of how getch() works? i mean , what to white inside brackets?

[JosAH]

[CENTER]

This is out of my current knowledge

No it is not; when/if your scanf() call doesn't return 1 (one), eat that offending
character and see how your program behaves.

kind regards,

Jos

[suzanna]

Thank you! I got it. you were very helpful. It took some brain storming but I finally got it.