Thread: endless loop for scanf - plz help

im trying to write a function that gets a number (int) from the user using scanf but for some reason the following code results in an endless loop. The point of the loop is to make sure the user enters a number and not a string:

Code:

//Function makes sure the user entered a valid entry
//and returns it
int Get_Line_Ammount()
{
	int amm_of_lines;
	int return_value;

	printf("How many lines do you want to store?: ");
	return_value = scanf("\n%d", &amm_of_lines);

	while (return_value == 0)
	{
		printf ("\nYou did not enter a valid number, Please re-enter: ");
		return_value = scanf("%d", &amm_of_lines);
	}

	return amm_of_lines;
}

pleazzzz, and thank you.

Hi,
The following line is your problem..both outside of the loop, and inside of it.

return_value = scanf("\n%d", &amm_of_lines);

you dont really need the "return_value =" part. replace other places you have 'return_value' with 'amm_of_lines'


hope that helps,
Deep

Originally Posted by owi_just

im trying to write a function that gets a number (int) from the user using scanf but for some reason the following code results in an endless loop. The point of the loop is to make sure the user enters a number and not a string:

Code:

//Function makes sure the user entered a valid entry
//and returns it
int Get_Line_Ammount()
{
	int amm_of_lines;
	int return_value;

	printf("How many lines do you want to store?: ");
	return_value = scanf("\n%d", &amm_of_lines);

	while (return_value == 0)
	{
		printf ("\nYou did not enter a valid number, Please re-enter: ");
		return_value = scanf("%d", &amm_of_lines);
	}

	return amm_of_lines;
}

pleazzzz, and thank you.

thanx for the try but again it created an enless loop.
any suggesstions?

I was thinking to keep it simple but then again, Im pretty new. See the following...
-Deep

Code:

int Get_Line_Ammount()
{
	int amm_of_lines;

                // this is your priming read
	printf("How many lines do you want to store?: ");
	scanf("%d", &amm_of_lines);

	while (amm_of_lines== 0)
	{
		// code here (for you to fill in) is similar to your priming read
	}

	return amm_of_lines;
}

sorry salem, i didnt mean the code that you gave me, i meant the one that DEEP posted, i didnt see yours at first

anyway, thanks for the tip it worked but in the specific exersize that im doing i cant declare a string, i have to do without it.

any suggestions?

Originally Posted by owi_just

sorry salem, i didnt mean the code that you gave me, i meant the one that DEEP posted, i didnt see yours at first

Actually, my code above worked perfectly fine for me..

i must be doing something else wrong then, maybe its outside the function

Originally Posted by owi_just

i must be doing something else wrong then, maybe its outside the function

possibly. feel free to post your full code, assuming it is not too long. In the meantime, about this function.. test it out on its own. Open a new .c file, and type the following...

Code:

#include <stdio.h>

int main()
{
  int test=0;

  printf("How many lines do you want to store?: ");
  scanf("%d", &test);

  while (test == 0)
  {
    printf("\n");
    printf("Cant enter zero, try again:  ");                
    scanf("%d", &test);
  }


  printf("\nThe number of lines is:  %d\n", test);
  return 0;
}

Compile that and run it. Hope now its starting to make some sense.

this is the copy/past of the output screen after i entered "hello" instead of a number:



Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:
Cant enter zero, try again:

Ah apologies for my "bad answer". Im new, and was just trying to help.

Salem, maybe you can provide the correct way to do it (without declaring a string)?