&...how important?

This is a discussion on &...how important? within the C Programming forums, part of the General Programming Boards category; Code: #include <stdio.h> int userNum = 0; /*Declare all variables*/ int main() { printf("Please enter a number: \n"); /*Ask for ...

  1. #1
    CAP
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    &...how important?

    Code:
    #include <stdio.h>
    
    int userNum = 0; /*Declare all variables*/
    
    int main()
    {
    	printf("Please enter a number: \n"); /*Ask for user input and record it to: userNum*/
    	scanf("%d",userNum);
    
    	if( userNum = 1)					/*Compare userNum to 1 and print corresponding answer*/
    
    	printf(" Your number equals 1" );
       
    	else
          printf(" Your number does not equal 1");
    
       
       return 0;
    }
    This message was supposed to be me asking for help with this program but I found the problem but came up with a question. In the above code I forgot the & sign right after scanf, no big deal just a typo but my compiler didn't catch it yet every time I ran the program it would crash and ask if I wanted to send an error report, can someone elaborate a bit on why it is so important but doesn't show up?

    P.S. Here is the fixed one:

    Code:
    scanf("%d",userNum);
    Code:
    scanf("%d", &userNum);
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  2. #2
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    What compiler are you using? It should have given you a warning about the following line like "Possibly incorrect assignment......".
    if( userNum = 1)
    You actually need two equal signs here ortherwise you are really assigning userNum to 1.

    change it to:
    if( userNum == 1)

    As for the "&" in the scanf in K&R second edition page 157 they state that all arguments after the formats must be pointers. Since you defined userNum as an int and not a pointer to an int you need to supply the "&" to reference the actual address of userNum and in effect make it a pointer.

    I can't believe your operating system didn't give you a "Null pointer assignment" error message without the "&".
    Last edited by jerryvtts; 07-16-2002 at 02:43 AM.

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