Thread: do-while doesn't work

Can anyone help with my do-while statement?
It doesn't work when input file name is blank (empty return).

Code:

if(argc == 1) // 0 & 1; only the program name is input 
{ 
do 
{ 
printf("\n Enter the input file name: "); 
fflush(stdin); 
gets(fileNameIn); 
} while (fileNameIn == NULL); 

printf("\n Enter the output file name: "); 
fflush(stdin); 
gets(fileNameOut); 
} ;

Your compiler realizes that you are brutalizing the C language, so it refuses to allow the code to work properly. Either that, or you're just doing some things horribly wrong. In the event it is the latter, allow me to help:

Code:

/**
*** Point #1: 'main' returns an 'int'. Period.
*** Anyone who tells you otherwise is wrong.
*** End of discussion.
***/

int main( int argc, char *argv[]) 
{ 
    /**
    *** Slight adjustment on your declaration. You can
    *** just use 0 here, or '\0', and while "\0" may work,
    *** it isn't the preferred way of doing it. Just remember
    *** this: single quotes for a single character.
    **/
    char fileNameIn[20] ={0}; 
    char fileNameOut[20] = {0}; 

    /**
    *** This will work also:
    **/
    if( argc < 2 )
    {
        do 
        { 
            printf("\n Enter the input file name: "); 
            /**
            *** 'fflush( inputStreamHere )' will not work the same
            *** on every compiler. Just because it works on one,
            *** doesn't mean it will work on another. It is not ANSI
            *** defined.
            *** 
            *** Never, ever, ever, use 'gets'. Use 'fgets' instead.
            *** 'gets' is unsafe because i could enter 80 characers in
            *** your buffer and trash your program.
            ***
            *** 'fileNameIn' will never equal NULL. fileNameIn[0] may
            *** be null, but that 'fileNameIn' still points to allocated
            *** memory. It is not a NULL poitner.
            **/
        } while( fgets( fileNameIn, 20, stdin ) == NULL );
    /**
    *** The ; you had here is not needed. Neither is this gets for
    *** the input file name. See below.
    **/
    }

    if ( argc == 2 || fileNameOut[0] == NULL )
    {
        printf("\n Please enter output file name: "); 
        fgets( fileOutName, 20, stdin );
        strncpy( fileNameIn, argv[1], 20 ); 
        fileNameIn[19] = NULL;
    }

    /**
    *** I prefer strncpy over strcpy due to it being safer.
    *** I manually make sure the last element is NULL.
    if ( argc == 3 )
    {    
        strncpy( fileNameIn, argv[1], 20 ); 
        strncpy( fileNameOut, argv[2], 20 );
        fileNameIn[19] = fileNameOut[19] = NULL;
    }

    printf("\n argc = %d\n", argc); 
    printf(" Program name = %s\n", argv[0]); 
    printf(" file name in = %s\n", fileNameIn); 
    printf(" file name out = %s\n", fileNameOut); 

    /**
    *** Since 'main' always returns an int, we return one.
    **/
    return 0;
}

Try that on for size. If you've any more questions, fire away.

Quzah.