C Programming - Structures, Unions, Enums - Discussion

#include<stdio.h>
int main()
{
printf("Weclome to IndiaBIX.com..!");
union var
{
int a;
float b;
};
union var v;
v.a=10;
v.b=20;
printf("%d\n", v.a);
return 0;
}

Output: Garbage value.

Union will take only the last value and other will be overwrite such as

main a
{

union v

{
int a,b,c;
}

union v h;
h.a=4;h.b=6;h.c=4;
printf("%d %d",h.a,h.c);

}

It will print only the last value 3

Output will be 3 3

But 'c' cannot create objects as java does so how it is possible?

All the members of union are stored at the same address, this means there is only one common memory. Hence in this case initially,

v.a = 10;//10 will be stored.
v.b = 20;//at the same address 20 will be stored.

#include<stdio.h>
int main()
{
union var
{
int a, b, c;
};
union var v;
v.a=10;
v.b=20;
printf("%d\n", v.c);
return 0;
}

Even if we add a third variable 'c' to the union and try to print it would output the same value =20 since it will always output the last value in such cases.

There are two concept first one is union by default preferred higher memory allocation, and second one is union has print single value and that value should be higher value.

Because union can initialize only one variable at a time.it will only one members that is greatest the number and last initialized members in aove programe v.a=10;

v.b=20; it will only 20 becoz union can occupy last members that is greatest number.

In C compiler allocates 2 bytes of memory to union and int needs 2 bytes. In this way first value is deleted and only 2nd value is present, in place of first value. So output is 20.

I didn't understand how it becomes 20 it must be 10.

Here you can see the difference:

You have to print value of 'a' before 'b' get declared to 20. Because union always display the datatype having larger memory.

#include<stdio.h>

int main()
{
union var
{
int a, b;
};
union var v;
v.a=10;
printf("%d\n", v.a);
v.b=20;

getch();
return 0;
}

The reason why union is used means it hold very less memory than structure it doesn't waste memory. I believe its a good think.