write code that reads the segment register settings

28. How do I write code that reads the segment register settings?

Ans: We can use segread( ) function to read segment register settings. There are four segment registers?code segment, data segment, stack segment and extra segment. Sometimes when we use DOS and BIOS services in a program we need to know the segment register's value. In such a situation we can use segread( ) function. The following program illustrates the use of this function.

#include 

main( )

{

struct SREGS s ;

segread ( &s ) ;

printf ( "\nCS: %X DS: %X SS: %X ES: %X",s.cs,

s.ds, s.ss, s.es ) ;

}

31. If we have declared an array as global in one file and we are using it in another file then why doesn't the sizeof operator works on an extern array?

Ans: An extern array is of incomplete type as it does not contain the size. Hence we cannot use sizeof operator, as it cannot get the size of the array declared in another file. To resolve this use any of one the following two solutions:

1. In the same file declare one more variable that holds the size of array. For example,

array.c

int arr[5] ;

int arrsz = sizeof ( arr ) ;

myprog.c

extern int arr[] ;

extern int arrsz ;

2. Define a macro which can be used in an array

declaration.

 For example,

myheader.h

#define SZ 5

array.c

#include "myheader.h"

int arr[SZ] ;

myprog.c

#include "myheader.h"

extern int arr[SZ] ;

33. How to find the row and column dimension of a given 2-D array?

Ans: Whenever we initialize a 2-D array at the same place where it has been declared, it is not necessary to mention the row dimension of an array. The row and column dimensions of such an array can be determined programmatically as shown in following program.

void main( )

{

int a[][3] = { 0, 1, 2,

9,-6, 8,

7, 5, 44,

23, 11,15 } ;

int c = sizeof ( a[0] ) / sizeof ( int ) ;

int r = ( sizeof ( a ) / sizeof ( int ) ) / c ;

int i, j ;

printf ( "\nRow: %d\nCol: %d\n", r, c ) ;

for ( i = 0 ; i <>

{

for ( j = 0 ; j <>

printf ( "%d ", a[i][j] ) ;

printf ( "\n" ) ;

}

}

34. The access( ) function...

The access( ) function checks for the existence of a file and also determines whether it can be read, written to or executed. This function takes two arguments the filename and an integer indicating the access mode. The values 6, 4, 2, and 1 checks for read/write, read, write and execute permission of a given file, whereas value 0 checks whether the file exists or not. Following program demonstrates how we can use access( ) function to check if a given file exists.

#include 

main( )

{

char fname[67] ;

printf ( "\nEnter name of file to open" ) ;

gets ( fname ) ;

if ( access ( fname, 0 ) != 0 )

{

printf ( "\nFile does not exist." ) ;

return ;

}

}

35. How do I convert a floating-point number to a string?

Ans: Use function gcvt( ) to convert a floating-point number to a string. Following program demonstrates the use of this function.

#include 

main( )

{

char str[25] ;

float no ;

int dg = 5 ; /* significant digits */

no = 14.3216 ;

gcvt ( no, dg, str ) ;

printf ( "String: %s\n", str ) ;

}

36. What is a stack ?

Ans: The stack is a region of memory within which our programs temporarily store data as they execute. For example, when a program passes parameters to functions, C places the parameters on the stack. When the function completes, C removes the items from the stack. Similarly, when a function declares local variables, C stores the variable's values on the stack during the function's execution. Depending on the program's use of functions and parameters, the amount of stack space that a program requires will differ.