if then else - newbie question

This is a discussion on if then else - newbie question within the C Programming forums, part of the General Programming Boards category; Still learning C, playing with if, then, else. In the program below, the final ELSE statement executes in every WHILE ...

  1. #1
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    if then else - newbie question

    Still learning C, playing with if, then, else. In the program below, the final ELSE statement executes in every WHILE loop. I'm not sure why. Program and output are below. I was thinking that at each getchar() in the WHILE loop, the program would pause, take in the input and then bounce back up to the WHILE evaluation. Thanks for your help.

    Jim

    Code:
    #import <Foundation/Foundation.h>
    
    int main (int argc, const char * argv[])
    {
    	char x;
    	
    	printf("Enter a, b or c (q to quit);\n");
    	x = getchar();
    	
    	while (x != 'q') {
    		if (x=='a') {
    			printf("Menu A\n");
    			x = getchar();
    		}
    		else if (x=='b'){
    			printf("Menu B\n");
    			x = getchar();
    		}
    		else if (x=='c'){
    			printf("Menu C\n");
    			x = getchar();
    		}
    		else {
    			printf("Not a valid option\n");
    			x = getchar();
    		}
    	}
    	
    	return(0);
    }
    And the output is:

    Running…
    Enter a, b or c (q to quit);
    a
    Menu A
    Not a valid option
    b
    Menu B
    Not a valid option
    d
    Not a valid option
    Not a valid option
    q

    Debugger stopped.
    Program exited with status value:0.

  2. #2
    and the Hat of Guessing tabstop's Avatar
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    Nov 2007
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    14,185
    Because the enter-key is neither a, nor b, nor c; therefore, when enter-key is read in, the final else switch is done.

  3. #3
    spurious conceit MK27's Avatar
    Join Date
    Jul 2008
    Location
    segmentation fault
    Posts
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    Yep. Read this:

    STDIN pitfalls

    Stuff about the "\n" newline from the enter key starts in the 4th paragraph.
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  4. #4
    Registered User
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    Apr 2010
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    Thanks! That now makes sense.

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