Thread: scanf

  1. #1
    Registered User
    Join Date
    Dec 2008


    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.
    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

    Last edited by Salem; 12-10-2008 at 11:39 AM. Reason: colour adds nothing, if it's all the same colour

  2. #2
    Jack of many languages Dino's Avatar
    Join Date
    Nov 2007
    Katy, Texas
    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.

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  3. #3
    Registered User
    Join Date
    Dec 2008
    thank u for such a prompt reply, it has been very helpful

  4. #4
    Registered User haseth's Avatar
    Join Date
    Dec 2008
    You can use flushall(); after your first scanf so that it only reads the first scanf and removes the second one from the buffer.

  5. #5
    C++ Witch laserlight's Avatar
    Join Date
    Oct 2003
    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.
    Quote Originally Posted by Bjarne Stroustrup (2000-10-14)
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