Monday, December 3, 2007

C Interview Questions

1. What is Polymorphism

'Polymorphism' is an object oriented term. Polymorphism may be defined as the ability of related objects to respond to the same message with different, but appropriate actions. In other words, polymorphism means taking more than one form. Polymorphism leads to two important aspects in Object Oriented terminology - Function Overloading and Function Overriding. Overloading is the practice of supplying more than one definition for a given function name in the same scope. The compiler is left to pick the appropriate version of the function or operator based on the arguments with which it is called. Overriding refers to the modifications made in the sub class to the inherited methods from the base class to change their behavior.

2. What is Operator overloading

When an operator is overloaded, it takes on an additional meaning relative to a certain class. But it can still retain all of its old meanings.Examples:1) The operators >> and <<>Dynamic Binding :The address of the functions are determined at runtime rather than @ compile time. This is also known as "Late Binding".

Static Binding :The address of the functions are determined at compile time rather than @ run time. This is also known as "Early Binding"

5. What is Difference Between C/C++

C does not have a class/object concept.
C++ provides data abstraction, data encapsulation, Inheritance and Polymorphism.
C++ supports all C syntax.
In C passing value to a function is "Call by Value" whereas in C++ its "Call by Reference"File extension is .c in C while .cpp in C++.(C++ compiler compiles the files with .c extension but C compiler can not!)
In C structures can not have contain functions declarations. In C++ structures are like classes, so declaring functions is legal and allowed.
C++ can have inline/virtual functions for the classes.
c++ is C with Classes hence C++ while in c the closest u can get to an User defined data type is struct and union

6. What will be the output of the following code?

void main ()
{ int i = 0 , a[3] ;
a[i] = i++;
printf ("%d",a[i]) ;

} The output for the above code would be a garbage value. In the statement a[i] = i++; the value of the variable i would get assigned first to a[i] i.e. a[0] and then the value of i would get incremented by 1. Since a[i] i.e. a[1] has not been initialized, a[i] will have a garbage value.

7. Why doesn't the following code give the desired result?

int x = 3000, y = 2000 ;

long int z = x * y ;
Here the multiplication is carried out between two ints x and y, and the result that would overflow would be truncated before being assigned to the variable z of type long int. However, to get the correct output, we should use an explicit cast to force long arithmetic as shown below: long int z = ( long int ) x * y ;
Note that ( long int )( x * y ) would not give the desired effect.

8. Why doesn't the following statement work?

char str[ ] = "Hello" ;
strcat ( str, '!' ) ;
The string function strcat( ) concatenates strings and not a character. The basic difference between a string and a character is that a string is a collection of characters, represented by an array of characters whereas a character is a single character. To make the above statement work writes the statement as shown below:
strcat ( str, "!" ) ;

9. How do I know how many elements an array can hold?

The amount of memory an array can consume depends on the data type of an array. In DOS environment, the amount of memory an array can consume depends on the current memory model (i.e. Tiny, Small, Large, Huge, etc.). In general an array cannot consume more than 64 kb. Consider following program, which shows the maximum number of elements an array of type int, float and char can have in case of Small memory model.

main( )
{
int i[32767] ;
float f[16383] ;
char s[65535] ;
}

10. How do I write code that reads data at memory location specified by segment and offset?

Use peekb( ) function. This function returns byte(s) read from specific segment and offset locations in memory. The following program illustrates use of this function. In this program from VDU memory we have read characters and its attributes of the first row. The information stored in file is then further read and displayed using peek( ) function.
#include
#include
main( )
{

char far *scr = 0xB8000000 ;
FILE *fp ;
int offset ;
char ch ;

if ( ( fp = fopen ( "scr.dat", "wb" ) ) == NULL )
{

printf ( "\nUnable to open file" ) ;
exit( ) ;

}

// reads and writes to file
for ( offset = 0 ; offset < fp =" fopen" offset =" 0">


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