C Programming

They both increment the variable. But the value returned by the pre-increment operator is the value of the variable after it has been incremented, while the value returned by the post-increment operator is the value before it has been incremented.

For example:

int a = 1;

int b = ++a;

// Now a is 2 and b is also 2.

int a = 1;

int b = a++;

// Now a is 2 but b is 1.

For example, suppose you free up a location before you're actually finished with it. Then further access to the location will either cause a run-time error (memory violation) or, what is worse (but more common), you will get access to a location that is being used for some completely unrelated purpose.

Trouble also occurs if you forget to free up some space. If you do this, you are losing the advantages of dynamic allocation. And in some circumstances - e.g. if you were writing the program that manages the space on a disk drive - this could be disastrous.

There are no surefire safeguards against these problems, you must be very careful when writing programs to return memory when you are finished with it, but not before.

Suppose that after using dynamic allocation for a while memory becomes fragmented thus:

bool isVowel(char c)

{

if ((c 'u'))

return true;

else

return false ;

}

A union is a way of providing an alternate way of describing the same memory area. In this way, you could have a struct that contains a union, so that the "static", or similar portion of the data is described first, and the portion that changes is described by the union. The idea of a union could be handled in a different way by having 2 different structs defined, and making a pointer to each kind of struct. The pointer to struct "a" could be assigned to the value of a buffer, and the pointer to struct "b" could be assigned to the same buffer, but now a->somefield and b->someotherfield are both located in the same buffer. That is the idea behind a union. It gives different ways to break down the same buffer area.

The difference between structure and union in c are: 1. union allocates the memory equal to the maximum memory required by the member of the union but structure allocates the memory equal to the total memory required by the members. 2. In union, one block is used by all the member of the union but in case of structure, each member have their own memory space

There is frequent rwquirement while interacting with hardware to access access a byte or group of bytes simultaneously and sometimes each byte individually. Usually union is the answer.

=======Difference With example***** Lets say a structure containing an int,char and float is created and a union containing int char float are declared. struct TT{ int a; float b; char c; } Union UU{ int a; float b; char c; }

sizeof TT(struct) would be >9 bytes (compiler dependent-if int,float, char are taken as 4,4,1)

sizeof UU(Union) would be 4 bytes as supposed from above.If a variable in double exists in union then the size of union and struct would be 8 bytes and cumulative size of all variables in struct.

{

char c;

long l;

char *p;

};

union bar

{

char c;

long l;

char *p;

};

A struct foo contains all of the elements c, l, and p. Each element is

separate and distinct.

A union bar contains only one of the elements c, l, and p at any given

time. Each element is stored in the same memory location (well, they all

start at the same memory location), and you can only refer to the element

which was last stored. (ie: after "barptr->c = 2;" you cannot reference

any of the other elements, such as "barptr->p" without invoking undefined

behavior.)

Try the following program. (Yes, I know it invokes the above-mentioned

"undefined behavior", but most likely will give some sort of output on

most computers.)

======= Union allocates the memory equal to the maximum memory required by the member of the union but structure allocates the memory equal to the total memory required by the members. In union,one block is used by all the member of the union but in case of structure, each member have their own memory space.

Union allocates the memory equal to the maximum memory requried by the member of the union but structure allocates the memory equal to sum of the memory allocated to its each individual members.

In Union, one block is used by all the member of union but in case of structure, each member have their own memory space.

Union allocates the memory equal to the maximum memory requried by the member of the union but structure allocates the memory equal to total memory requried by the members. In Union, one block is used by all the member of union but in case of structure, each member have their own memory space.