infinite loop

This is a discussion on infinite loop within the C Programming forums, part of the General Programming Boards category; Hi: Could someone please help? I want to check if input valid or not. But my code doesn't stop as ...

  1. #1
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    infinite loop

    Hi:

    Could someone please help?

    I want to check if input valid or not. But my code doesn't stop as expected.

    Code:
    void validateSex(char sex) {
       if ( sex != 'M' || sex != 'F') {
         printf("Input Error: Invalid \n");
    
         do {
           printf("Enter your sex (M or F): ");
           scanf("%c", &sex);
         }while (sex !='M' || sex!='F');
       }; /* End if */
    }
    whats wrong with it?

    Thanks

  2. #2
    and the hat of wrongness Salem's Avatar
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    > while (sex !='M' || sex!='F')
    sex = M, so sex != 'F' is true, so round the loop you go.
    sex = F, so sex != 'M' is true, so round the loop you go.

    Perhaps && instead.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
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  3. #3
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    > if ( sex != 'M' || sex != 'F') {
    That's always true.

  4. #4
    Hacker MeTh0Dz's Avatar
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    Your current implementation is using an unnecessary do loop and if statement. If you are going to evaluate if it is true or false before the do loop anyways, there is no reason to even use it. Just use a while loop instead.

    Code:
    void validateSex(char sex) {
    	while (sex !='M' && sex !='F') {
    		printf("Enter your sex (M or F): ");
    		scanf("%c", &sex);
    	}
    }

  5. #5
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    Thanks for your help.

    Problem solved.

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