Compiler error: Cannot modify a constant value.
p is a pointer to a "constant integer". But we tried to change the value of
the "constant integer".
s[i], *(i+s), *(s+i), i[s] are all different ways of expressing the same idea.
Generally array name is the base address for that array. Here s is the base address. i is
the index number/displacement from the base address. So, indirecting it with * is same as
s[i]. i[s] may be surprising. But in the case of C it is same as s[i].
I hate U
For floating point numbers (float, double, long double) the values cannot
be predicted exactly. Depending on the number of bytes, the precession with of the value
represented varies. Float takes 4 bytes and long double takes 10 bytes. So float stores 0.9
with less precision than long double.
Rule of Thumb:
Never compare or at-least be cautious when using floating point numbers
with relational operators (== , >, <, <=, >=,!= ) .
5 4 3 2 1
When static storage class is given, it is initialized once. The change in the
value of a static variable is retained even between the function calls. Main is also treated
like any other ordinary function, which can be called recursively.
2 2 2 2 2 2 3 4 6 5
Initially pointer c is assigned to both p and q. In the first loop, since only
q is incremented and not c , the value 2 will be printed 5 times. In second loop p itself is
incremented. So the values 2 3 4 6 5 will be printed.
Linker Error : Undefined symbol '_i'
extern storage class in the following declaration,
extern int i;
specifies to the compiler that the memory for i is allocated in some other program and
that address will be given to the current program at the time of linking. But linker finds
that no other variable of name i is available in any other program with memory space
allocated for it. Hence a linker error has occurred .
0 0 1 3 1
Logical operations always give a result of 1 or 0 . And also the logical
AND (&&) operator has higher priority over the logical OR (||) operator. So the
expression ‘i++ && j++ && k++’ is executed first. The result of this expression is 0
(-1 && -1 && 0 = 0). Now the expression is 0 || 2 which evaluates to 1 (because OR
operator always gives 1 except for ‘0 || 0’ combination- for which it gives 0). So the value
of m is 1. The values of other variables are also incremented by 1.
The sizeof() operator gives the number of bytes taken by its operand. P is
a character pointer, which needs one byte for storing its value (a character). Hence sizeof
(*p) gives a value of 1. Since it needs two bytes to store the address of the character
pointer sizeof(p) gives 2.
-1 is internally represented as all 1's. When left shifted four times the least
significant 4 bits are filled with 0's.The %x format specifier specifies that the integer
value be printed as a hexadecimal value.
Compiler Error : Type mismatch in redeclaration of function display
In third line, when the function display is encountered, the compiler
doesn't know anything about the function display. It assumes the arguments and return
types to be integers, (which is the default type). When it sees the actual function display,
the arguments and type contradicts with what it has assumed previously. Hence a compile
time error occurs.
Here unary minus (or negation) operator is used twice. Same maths rules
applies, ie. minus * minus= plus.
However you cannot give like --2. Because -- operator can only be
applied to variables as a decrement operator (eg., i--). 2 is a constant and not a variable.
Since the #define replaces the string int by the macro char
In the expression !i>14 , NOT (!) operator has more precedence than ‘ >’
symbol. ! is a unary logical operator. !i (!10) is 0 (not of true is false). 0>14 is false
p is pointing to character '\n'. str1 is pointing to character 'a' ++*p. "p is pointing
to '\n' and that is incremented by one." the ASCII value of '\n' is 10, which is then
incremented to 11. The value of ++*p is 11. ++*str1, str1 is pointing to 'a' that is
incremented by 1 and it becomes 'b'. ASCII value of 'b' is 98.
Now performing (11 + 98 – 32), we get 77("M");
So we get the output 77 :: "M" (Ascii is 77).
p=&a you declare only two 2D arrays, but you are trying to
access the third 2D(which you are not declared) it will print garbage values. *q=***a
starting address of a is assigned integer pointer. Now q is pointing to starting address of
a. If you print *q, it will print first element of 3D array.
You should not initialize variables in declaration
The structure yy is nested within structure xx. Hence, the elements are of
yy are to be accessed through the instance of structure xx, which needs an instance of yy
to be known. If the instance is created after defining the structure the compiler will not
know about the instance relative to xx. Hence for nested structure yy you have to declare
The arguments in a function call are pushed into the stack from left to
right. The evaluation is by popping out from the stack. and the evaluation is from right to
left, hence the result.
the macro call square(4) will substituted by 4*4 so the expression
becomes i = 64/4*4 . Since / and * has equal priority the expression will be evaluated as
(64/4)*4 i.e. 16*4 = 64
++*p++ will be parse in the given order
• *p that is value at the location currently pointed by p will be taken
• ++*p the retrieved value will be incremented
• when ; is encountered the location will be incremented that is p++ will be executed
Hence, in the while loop initial value pointed by p is ‘h’, which is changed to ‘i’ by
executing ++*p and pointer moves to point, ‘a’ which is similarly changed to ‘b’ and so
on. Similarly blank space is converted to ‘!’. Thus, we obtain value in p becomes “ibj!
gsjfoet” and since p reaches ‘\0’ and p1 points to p thus p1doesnot print anything.
Preprocessor executes as a seperate pass before the execution of the
compiler. So textual replacement of clrscr() to 100 occurs.The input program to compiler
looks like this :
100; is an executable statement but with no action. So it doesn't give any
Some address will be printed.
Function names are just addresses (just like array names are addresses).
main() is also a function. So the address of function main will be printed. %p in printf
specifies that the argument is an address. They are printed as hexadecimal numbers.
The first clrscr() occurs inside a function. So it becomes a function call. In
the second clrscr(); is a function declaration (because it is not inside any
enum assigns numbers starting from 0, if not explicitly defined.
the second pointer is of char type and not a far pointer
printf takes the values of the first two assignments of the program. Any
number of printf's may be given. All of them take only the first two
values. If more number of assignments given in the program,then printf
will take garbage values.
* is a dereference operator & is a reference operator. They can be
applied any number of times provided it is meaningful. Here p points to
the first character in the string "Hello". *p dereferences it and so its value
is H. Again & references it to an address and * dereferences it to the
Compiler error: Undefined label 'here' in function main
Labels have functions scope, in other words The scope of the labels is
limited to functions . The label 'here' is available in function fun() Hence it
is not visible in function main.
Compiler error: Lvalue required in function main
Array names are pointer constants. So it cannot be modified.
Output Cannot be predicted exactly.
Side effects are involved in the evaluation of i
The expression i+++++i is parsed as i ++ ++ + i which is an illegal
combination of operators.
Compiler Error: Constant expression required in function main.
The case statement can have only constant expressions (this implies that
we cannot use variable names directly so an error).
Enumerated types can be used in case statements.
Scanf returns number of items successfully read and not 1/0. Here 10 is
given as input which should have been scanned successfully. So number
of items read is 1.
before entering into the for loop the checking condition is "evaluated".
Here it evaluates to 0 (false) and comes out of the loop, and i is
incremented (note the semicolon after the for loop).
p is pointing to character '\n'.str1 is pointing to character 'a' ++*p
meAnswer:"p is pointing to '\n' and that is incremented by one." the ASCII
value of '\n' is 10. then it is incremented to 11. the value of ++*p is 11.
++*str1 meAnswer:"str1 is pointing to 'a' that is incremented by 1 and it
becomes 'b'. ASCII value of 'b' is 98. both 11 and 98 is added and result is
subtracted from 32.
Initialization should not be done for structure members inside the structure
in the end of nested structure yy a member have to be declared.