quick guide

Objective Type Questions in Managing Input & Output Functions: C language:-


What will be the output of the following programs:
1.main()
{
static char str[] ="Academy"
printf("%s\n%s",str,"Acemedy");
}
a. Academy Academy b.Error
c.No Error d.None

Output: Academy Acamedy

Explanation: We know that mentioning the name of a
string yields the base address of the string.When this
base address is passed to printf() it prints out each
character in the string till it encounters '\0' sitting
at the end of the string.A string written double quotes
also gives the base address of the string.This base
address when passed to printf() would result in printing
"Acemedy"once again.

2. main()
{
float a=3.14;
printf("%\na=%f",a);
printf("%\na=%6.2f",a);
printf("%\na=%-6.2f",a);
printf("%\na=%6.1f",a);
printf("%\na=%6.0f",a);
}

Output: a=3.140000
a= 3.14
a=3.14
a= 3.1
a= 3

Explanation: The first printf() uses the format
specification for a float,hence a gets printed as
3.140000, as bydefault a float is printed with 6
decimal places.In the next printf() the number that
precedes the f in %f is an optional specifier,which
governs how exactly the varible is to be printed 6.2
signifies that the field width i.e the total number
of columns that the values occupies on the screen,
should be 6 and that the value should have 2 digits
after the decimal point.Thus 3.14 is printed with
blank spaces on the left,that is with right
justification.

For left justification,we use a minus sign with
the specifiers,as is done in the next printf().It
prints the value of a starting from the zeroth column
,with only 2 decimal digits.The specification 6.1
prints 3.1 with right justification.
In the last printf(),6.0 specifies zero decimal
digits,have only 3 is dsplayed right justified.

3. main()
{
printf("%20s\n","short leg");
printf("%20s\na","long leg");
printf("%20s\n","deep fine leg");
printf("%20s\n","backward short leg");
printf("%20s\n","legs all the same!");
}

Output: shortleg
longleg
deep fine leg
backward short leg
legs all the same!

Explanation: The output is right justified,as the field
width specified with each %s is plus 20.For each string,
20 column are set aside,and the strings are printed with
blanks filling up the remaining columns are on the left.

4. main()
{
printf("hello\nhi\n");
printf("hello\rhi");
}

Output: hello
hi
hillo

Explanation: The escape sequence '\n' called new line
takes the cursor to the beginning of the next line.Hence
with the first printf() "hello" and "hi" are printed on
consective lines.A '\r' on the other hand,takes the cursor
to the beginning of the same line in which the cursor is
currently present.Hence,having printed "hello",the cursor
is sent back at 'hi' is printed.The first two letters of
"hello" are therefore written over,and we get the output
as "hillo".

5. main()
{
printf("%hello\b\b\b\b\b");
printf("hi\b\b\bbye");
}

Output: byelo

Explanation: The escape sequence '\b' stands for backspace
which takes the cursor to the previous character.In the
first printf(), "hello" is printed, following which the
cursor is positioned after 'o'.Now the 5 backspaces take
the cursor to the letter 'h' of "hello".The control now
passes to the second printf(),and "hi" is written over the
first three characters of "hello" resulting in "hilo".Once
again 3 backspaces are encountered,which take the cursor
back at 'h' of "hi".Next "bye" is printed on top of "hi".
The "lo" that is seen has persisted from the first printf()'s.
"hello", as it never got overwritten.Hence the output "byelo".

6.main()
{
printf(" i\tam\ta\tboy");
}

Output:i am a boy

Explanation: The message is printed with space inserted
wherever the escape sequence '\t' occured. This sequence
stands for a tab.In one compiler,the tabs had been setup
after every 5 colunms,at 0,5,10 etc.Hence while executing
printf(),when '\t' is encountered,the cursor skips to the
immediately next column which is a multiple of 5,and then
prints the next word.Thus 'i' is printed form the 15th
column,"am" from the 5th,'a' from the 10th,and "boy" from
the 15th column.Some compilers like turbo c allow you to
change the tab settings,so that the tab widths can set up
as desired.

7. #include
main()
{
char str1[30],str2[30];
printf("enter a sentence \n");
scanf("%s",str1);
printf("%s",str2);
fflush(stdin);
printf("\n enter a sentence \n");
gets(str2);
printf("%s",str2);
}
Output: enter a sentence
nothing succeeds like success
enter a sentence
nothing succeeds like success
nothing succeeds like success

Explanation: The scanf() suffers from the limitation that a
maximum of only one word can be accepted by it.The moment a
space(or a tab or a newline)is typed,scanf() assumes you have
finished supplying information ,and hence ignores whatever
follows.That's why,str[] stroes only "Nothing,as it is proved
by the first output.To overcome this limitation,we have an
unformatted console i/o function called gets().It accepts
whatever u type from the keyboard till the enter key is hit.
To be precise,get() accepts everything until a '\n' is
encountered,which it replaces with a '\0' .
Thus the entire string that we entered is obtained in the
second output.fflush() flushes out the current keyboard buffer
would be read by gets() .Since gets() is terminated on reading
an enter key ,u won't get a chance to supply the 2nd sentence.

8. #include
main()
{
char name[20],name1[20];
int age,age1;
printf("enter name and age\n");
scanf("%s%d",name,&age);
printf("%s%d",name,age);
printf("\n enter name and age\n");
fscanf("stdin,"%s%d",name1,&age1);
printf("stdout,"%s%d",name1,age1);
}

Output: enter name and age
raj 18
enter name and age
anjali 21

Explanation: Here the first set of statement comprising of
prinf()s and scanf() is fairly simple.The fscanf() and
fprintf() that follow next need some explaning.
Fscanf( ) like scanf(),is used for formatted reading
of data. The only difference is that the former takes an
additional arugement that of a file pointer.This pointer
indicates to the fscanf() from where the data is to be read.
whereas scanf() is capable of reading data onlyfrom the
keyboard.In the call to fsacnf() the file pointer stdin is
being used ,which sands for standard input device i.e the
keyboard.Since stdin is a pointer to a standard file,we do
not need to use fopen() to open it,as it is always open for
reading.The counterpart of fscanf() is fprintf().

It too needs a file pointer as its first argument.
Here the file pointer used is stdout,which stands for
standard output device,i.e the display monitor.Thus using
stdin in fscanf() and stdout in fprint() makes them them work
like the familiar scanf() and printf() functions.Hence both
the sets collect the names and ages from keyboard.