some questions

[VishalNikiSharma]

Dear Gurus
i came across some questions please help me to understand those questions:

1>
int x;
while(x<100)
{
cout<<x;
x++;
}

2>
void afunction()
{
if(1)
{
break;
a_function();
cout<<"Err";
}
}

3>
void afunction(int *x)
{
x=new int;
*x=12;
}
int main()
{
int v=10;
afunction(&v);
cout<<v;
}

4>
Would you rather wait for the results of a quicksort, a linear search, or a bubble sort on a 200000 element array?
Quicksort
Linear Search
Bubble Sort

5> what is difference between endl and /n

6> what is the order in which the following is executed
!(1 &&0 || !1)
!(1&&1||1&&0)

i think answer should be

1>
0 1 2 upto 99

2>
exit from if block

3>
12

4>
no guesses

5>no difference
6>??

the answers which the site from where i took these question are different,please help me to understand the answer
thanks in advance
bye
vishal sharma

[Graham]

1. Note that x is not initialised.

2.

3. Consider for a moment the difference between pass-by-value and pass-by-pointer. How many "*"s do you need to allow a change within the function to get outside the function? If I have "f(int i)", will any change to i from within f() be seen after f() returns? If I have "f(int * i)", will a change to *i be seen outside the function? What about a change to i?

4. Look up descriptions of the various types of sort.

5. endl is a stream manipulator - it is a class-type object. '\n' is just a character. What does that imply for endl?

6. Read up on operator precedence and evaluation order.

[VishalNikiSharma]

dear graham
thanks for ur reply but according to me for the question number 3
as we are using
f(int *x)
which i thinks is passing by reference so value should be 12 and not 10 as mentioned in the reference site?

and for question 2
the answer is complier error but my thinking is that there is no error
i am not getting how there is error
vishal

[Graham]

Question 2 - what does break break out of? Hint: Is an if statement a loop?

Question 3 - Read my hints again. If I have f(int* i), and inside that I assign a value to i (not *i), does the change in i get seen outside the function? For example:

void f(int* i)
{
    i = new int;
}

int main()
{
    int *p = 0;
    f(p);
}

After the call to f(), does p point to valid memory, or is its value 0? Compare that with

void f(int i)
{
    i = 10;
}

int main()
{
    int i = 0;
    f(i);
}

After the call to f(), does i have the value 0 or 10?

[VishalNikiSharma]

graham
thanks for helping me to understand the question number 2
but sorry still for question number 3
suppose my code is like this

int f(int *i)
{
*i = 10;
}
int main()
{
int n;
n = 1;
cout<<n;
f(n);
cout<<n;
return 0;
}
according to me for this answer should be
1
10
as i am passing as reference

now is using

i = new int;

makes some difference

as far as ur question is concerned i think in case 2 answer will be 0
and for case 1 answer (should?) be some garbage value
i am not sure...
sorry for troubling u but please continue to help me..

[Graham]

OK.

When you write a definition like:

void f(int i)
{
    i = 10;
}

You are declaring a local variable called i in the function f(). When you call f(), that local variable is initialised with whatever value you give as an argument to the call. So, if you call f(n), say, then i is initialised with the current value of n. Note: this means that i inside the function is a copy of n outside the function. If you modify i, you are changing the copy not the original. So, if I have

n= 2;
f(n);

When it first enters the function f(), i has the value 2 (a copy of the argument). f() then changes the value of its local variable. But this does not change n, it only changes the copy so, after the call, n still has the value 2.

Similarly, if I now have

void g(int *p)
{
    *p = 10;
}

If I call g() with a pointer-to-int, the variable p (local to g()), is initialised with that value - it's a copy again. Now, because we're dealing with pointers, the original and the copy both point to the same thing. Therefore, if I modify the pointed-to object with either the original or the copy, it will be modified.

So,

int n = 2;
g(&n);

after the call to g(), n has the value 10 because we changed it via a copy of its address. Note the difference between f(n) and g(&n). When we call g(), the argument is &n, not n. That's because we don't give n to g(), we give the address of n (i.e. a pointer to n).
OK, now let's consider

void h(int *p)
{
    p = new int;
    *p = 10;
}

int main()
{
    int n = 2;
    h(&n);
}

When we call h(), the variable p (local to h()) is intialised with a copy of the argument (the address of n). So, on entry to h(), p points to n and we could change the value of n by assigning to *p. However, what we do is to change the value of p by assigning to it the address of some newly allocated memory. Remember, we are assigning to a copy - the original value (the address of n) does not get changed. We now put the value 10 into that newly-allocated bit of memory (not into n). When h() exits, the variable p is lost and we can no longer refer to the memory that we new'd in the function (this is called a memory leak - memory has been allocated but we don't know where it is any more). But, because h() changed p, n in main() was unaffected by anything we did to *p - p no longer pointed at n.
Now to take your last bit of code:

int f(int *i)
{
    *i = 10;
}
int main()
{
    int n;
    n = 1;
    cout<<n;
    f(n);
    cout<<n;
    return 0;
}

This will not compile. the function f() wants a pointer-to-int as its argument. When you call it, you are supplying an int. The two are not compatible, so the compiler flags an error.

[VishalNikiSharma]

Thanks graham
now i am able to get what u intented
graham i like to be expert in c/c++ like u,give me any suggestion...

[Graham]

Time.........

I started with FORTRAN 20+ years ago, moved on to C about 15 years ago, then C++ about 8 years ago. Read good books and listen to people who know. There's no magic, only experience.

[VishalNikiSharma]

Graham
is a comma operator a LHS or RHS operator
i mean to say
if a = 10,20,30,40,50
then a is 10 or 50?
i think it should be 50???is it?
vishal sharma

[Gabriel Fleseriu]

Directly out of MSDN:
The comma operator has left-to-right associativity. Two expressions separated by a comma are evaluated left to right. The left operand is always evaluated, and all side effects are completed before the right operand is evaluated.

Consider the expression

e1 , e2

The type and value of the expression are the type and value of e2; the result of evaluating e1 is discarded. The result is an l-value if the right operand is an l-value.

graham i like to be expert in c/c++ like u,give me any suggestion...

Trying to find out answers by yourself will gain you experience.