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C programming help *Solved, lock please*
RHerms716
Registered User regular
Registered User regular
So I have a final coming up for my intro to C programming class, and after looking over the practice exams, there are a few topics I am still a bit weak on. I guess I have the most trouble with variable types and pointers.
Can anyone help explain a few of these questions? Thanks!
EDIT: After looking at the 2nd problem, is the error that the function is void, yet requires a return value?
Can anyone help explain a few of these questions? Thanks!
Find the error.
/*
* print the given string to stdout character by character,
* followed by a line feed
*/
void
print string (char* string)
{
while (’\0’ != *(string++)) {
printf ("%c", *string);
}
printf ("\n");
}
Find the error.
/* choose one of two strings to be printed */
void
string
select (int which)
{
char str1[8] = "string1";
char str2[8] = "string2";
switch (which) {
case 1:
return str1;
case 2:
return str2;
default:
return str1;
}
}
/* no errors in main -- included as a hint for string select */
int
main ()
{
char* s;
s = string
select (1);
printf ("string is %s\n", s);
return 0;
}
Find the error.
static unsigned char digit[10] = {
0x77, 0x41, 0x6E, 0x6B, 0x59, 0x3B, 0x3F, 0x61, 0x7F, 0x79
};
unsigned char
pick_display ()
{
int num;
printf ("What number should appear on the 7-segment display? ");
if (1 != scanf ("%d", &num)) {
num = 0;
}
return digit[num];
}
EDIT: After looking at the 2nd problem, is the error that the function is void, yet requires a return value?
RHerms716 on
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Posts
Edit: The second one doesn't even really make sense. The program as quoted will always print the exact same information, because the function call isn't changing anything. Yes, the function should be char* instead of void because it's returning a char array. But even then, the program won't work as expected because there IS an error in main (despite the comment). Because if the function is returning a string, then we need to set some variable to that string and then display it, otherwise the main function always prints the same thing.
Not sure what's up with the third one... I think it works... but those ascii codes aren't digits, and one of them I believe is the DEL code.
Hmm... those ascii codes seem to be encoded information on the way that the bars in a 7 segment LED display should be lit. For example, take digit[0]. On a 7 segment display, 6 bars are lit to display the number "0", and you'll notice that 6 bits are set in 0x77. Similarly, 2 bars are lit to show the number "1", and only two bits are set in digit[1]. If you're especially keen, you can figure out which bits correspond to which bar in the 7 seg display they're using.
The only real issue that's flagged for me when I skimmed through the third example is the lack of bound checking.
Anyway, the 3rd example does scanf(), which is, of course, vulnerable to buffer overflows. I don't know if that's an "error" per se, though using scanf() to get one character from stdin is certainly an "error" in judgment.
This can be locked.