scanf

cProgNoob · 12-10-2008, 07:01 AM

I am very new to c programming and dont mean to be wasting anyones time but after trying to use the scanf function I am having some difficulties. I have created much more intracate programs (which isnt hard I know) but i havent used scanf, and I really cant see how this is going wrong.

Code:

int main(void){

	int no, valid;
	
	printf("\nHow many would you like?\n\n           ");
	
	if(scanf("%d",&no) != 1){ // Checking to see only one argument has been entered
	
		printf("\nOnly one value.\n");
		return (EXIT_FAILURE);
		
	}
	
	valid = scanf("%d",&no);
	valid = ((valid != 0) && (valid != EOF));
	
	if( !valid ){ // Checking to see the correct data type has been entered
	
		printf("\nMust be an integer.\n");
		return (EXIT_FAILURE);
		
	}	
	
	return (EXIT_SUCCESS);
	
}

The error checks seem to not be working.

when I type in 'a 2 ' it prints 'Only one value' but when I type '2 a' it prints 'Must be an integer'. But in both instances I am expecting 'Only one value' to be printed.

Sorry for such a trivial problem but any help would be much appreciated

Cheers

Dino · 12-10-2008, 07:14 AM

When you enter '2 a', the first scanf() only sucks in the 2 and leaves the a in the input buffer because scanf() is smart enough (dumb enough?) to stop parsing at the first whitespace it encounters. So the 'a' is left for your second scanf() to pull.

cProgNoob · 12-10-2008, 08:16 AM

thank u for such a prompt reply, it has been very helpful

haseth · 12-10-2008, 10:58 AM

You can use flushall(); after your first scanf so that it only reads the first scanf and removes the second one from the buffer.

**laserlight** · 12-10-2008, 11:04 AM

Quote:

Originally Posted by haseth

You can use flushall(); after your first scanf so that it only reads the first scanf and removes the second one from the buffer.

Unfortunately flushall() does not appear to exist in the C standard library or cProgNoob's code.

12-10-2008, 07:01 AM	#1
cProgNoob Registered User Join Date: Dec 2008 Posts: 2	scanf I am very new to c programming and dont mean to be wasting anyones time but after trying to use the scanf function I am having some difficulties. I have created much more intracate programs (which isnt hard I know) but i havent used scanf, and I really cant see how this is going wrong. Code: int main(void){ int no, valid; printf("\nHow many would you like?\n\n "); if(scanf("%d",&no) != 1){ // Checking to see only one argument has been entered printf("\nOnly one value.\n"); return (EXIT_FAILURE); } valid = scanf("%d",&no); valid = ((valid != 0) && (valid != EOF)); if( !valid ){ // Checking to see the correct data type has been entered printf("\nMust be an integer.\n"); return (EXIT_FAILURE); } return (EXIT_SUCCESS); } The error checks seem to not be working. when I type in 'a 2 ' it prints 'Only one value' but when I type '2 a' it prints 'Must be an integer'. But in both instances I am expecting 'Only one value' to be printed. Sorry for such a trivial problem but any help would be much appreciated Cheers Last edited by Salem; 12-10-2008 at 11:39 AM. Reason: colour adds nothing, if it's all the same colour
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12-10-2008, 07:14 AM	#2
Dino Jack of many languages Join Date: Nov 2007 Location: Katy, Texas Posts: 1,929	When you enter '2 a', the first scanf() only sucks in the 2 and leaves the a in the input buffer because scanf() is smart enough (dumb enough?) to stop parsing at the first whitespace it encounters. So the 'a' is left for your second scanf() to pull. __________________ Mac and Windows cross platform programmer. Ruby lover. Memorable Quotes From Recent Posts: I can't remember.
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12-10-2008, 08:16 AM	#3
cProgNoob Registered User Join Date: Dec 2008 Posts: 2	thank u for such a prompt reply, it has been very helpful
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12-10-2008, 10:58 AM	#4
haseth Registered User Join Date: Dec 2008 Posts: 4	You can use flushall(); after your first scanf so that it only reads the first scanf and removes the second one from the buffer.
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