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FALSE & TRUE undeclared???

This is a discussion on FALSE & TRUE undeclared??? within the C Programming forums, part of the General Programming Boards category; Why it says TRUE and FALSE are undeclared?? How to declare?? What I'm doing wrong? Code: #define s 256 main() ...

  1. #1
    Registered User Makara's Avatar
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    FALSE & TRUE undeclared???

    Why it says TRUE and FALSE are undeclared?? How to declare?? What I'm doing wrong?
    Code:
    #define s 256
    main()
    {
        char answer, t[s];
        char stop;
    
        stop = FALSE;
        while (stop = FALSE)
        {
            printf("Enter: ");
            gets(t);
            while (answer != 'Y'||answer != 'N')
            {
                printf("Continue?");
                answer = getchar();
            }
            if (answer = 'N')
            {
                stop = TRUE;
            }
        }
        system("PAUSE");
    18 `FALSE' undeclared (first use in this function)
    33 `TRUE' undeclared (first use in this function)
    Last edited by Makara; 02-21-2012 at 09:42 AM.

  2. #2
    Registered User
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    Long Beach, CA
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    TRUE and FALSE are not keywords in C. It is common for people to declare them to make code more readable however. Remember, in C, zero is false and anything else is true, so you can just #define FALSE as 0 and TRUE as 1.

    EDIT: If you have a C99 compliant compiler, and you #include <stdbool.h>, you will actually have a bool type with true and false (lowercase).

  3. #3
    Registered User hk_mp5kpdw's Avatar
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    Other nits:
    Code:
    while (stop = FALSE)
    ...
    if (answer = 'N')
    Be aware there is a difference between = (assignment) and == (equality test).





    Code:
    char answer, t[s];
    ...
    answer = getchar();
    Note that getchar returns an int but in this case it does not look too critical that it be so. In other cases it does become important to use the proper type and as such you should get into the habit.





    Code:
    gets(t);
    Avoid gets as it is susceptible to buffer overruns, prefer to use the fgets function instead which has protections against this.





    Code:
    main()
    You should explicitly state main as returning an int and do so at the end of the function.
    iMalc likes this.
    "Owners of dogs will have noticed that, if you provide them with food and water and shelter and affection, they will think you are god. Whereas owners of cats are compelled to realize that, if you provide them with food and water and shelter and affection, they draw the conclusion that they are gods."
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  4. #4
    a_capitalist_story
    Join Date
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    By the way, this:

    Code:
    while (stop = FALSE)
    and this:

    Code:
    if (answer = 'N')
    are *assignments*, not *comparisons". You use == to compare two (non-array) variables.

    And get rid of gets(), it should never be used. Check the FAQ.

    Edit: ninja'd

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