How to obtain a path of the given file?
The function searchpath( ) searches for the specified file in the subdirectories of the current path. Following program shows how to make use of the searchpath( ) function.#include “dir.h”
void main ( int argc, char *argv[] )
{
char *path ;
if ( path = searchpath ( argv[ 1 ] ) )
printf ( “Pathname : %s\n”, path ) ;
else
printf ( “File not found\n” ) ;
}
Can we get the x and y coordinate of the current cursor position ?
The function wherex( ) and wherey( ) returns the x-coordinate and y-coordinate of the current cursor position respectively. Both the functions return an integer value. The value returned by wherex( ) is the horizontal position of cursor and the value returned by wherey( ) is the vertical position of the cursor. Following program shows how to use the wherex( ) and wherey( ) functions.#include
main( )
{
printf ( “Just\n To\n Test\n Where\n the cursor\n goes” ) ;
printf ( “Current location is X: %d Y: %d\n”, wherex( ), wherey( ) ) ;
}
How to obtain the current drive through C ?
We can use the function _getdrive( ) to obtain the current drive. The _getdrive( ) function uses DOS function 0X19 to get the current drive number#include
main( )
{
int disk ;
disk = _getdrive( ) + ‘A’ - 1 ;
printf ( “The current drive is: %c\n”, disk ) ;
}
How to restrict the program’s output to a specific screen region?
A C function window( ) can be used to restrict the screen output to a specific region. The window( ) function defines a text-mode window. The parameters passed to this function defines the upper-left and lower-right corner of the region within which you want the output. In the following program, the string ‘Hello!’ gets printed within the specified region. To print the string we must use cprintf( ) function which prints directly on the text-mode window.#include
main( )
{
int i, j ;
window ( 20, 8, 60, 17 ) ;
for ( i = 0 ; i < 8 ; i++ )
for ( j = 0 ; j < 10 ; j++ )
cprintf ( “Hello!” ) ;
}
How do I print the contents of environment variables?
The following program shows how to achieve this:main( int argc, char *argv[ ], char *env[ ] )
{
int i = 0 ;
clrscr( ) ;
while ( env[ i ] )
printf ( “\n%s”, env[ i++ ] ) ;
}
main( ) has the third command line argument env, which is an array of pointers to the strings. Each pointer points to an environment variable from the list of environment variables.
What’s the difference between these two declarations?
struct str1 { … } ;typedef struct { … } str2 ;
Ans : The first form declares a structure tag whereas the second declares a typedef. The main difference is that the second declaration is of a slightly more abstract type — its users don’t necessarily know that it is a structure, and the keyword struct is not used when declaring instances of it.
How do I convert a floating-point number to a string?
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 ) ;
}
How to find the row and column dimension of a given 2-D array?
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 < r ; i++ )
{
for ( j = 0 ; j < c ; j++ )
printf ( “%d “, a[i][j] ) ;
printf ( “\n” ) ;
}
}
How do I write printf( ) so that the width of a field can be specified at runtime?
This is shown in following code snippet.main( )
{
int w, no ;
printf ( “Enter number and the width for the
number field:” ) ;
scanf ( “%d%d”, &no, &w ) ;
printf ( “%*d”, w, no ) ;
}
Here, an ‘*’ in the format specifier in printf( ) indicates that an int value from the argument list should be used for the field width.
Are the following two statements identical?
char str[6] = “Kicit” ;char *str = “Kicit” ;
Ans: No! Arrays are not pointers. An array is a single, pre-allocated chunk of contiguous elements (all of the same type), fixed in size and location. A pointer on the other hand, is a reference to any data element (of a particular type) located anywhere. A pointer must be assigned to point to space allocated elsewhere, but it can be reassigned any time. The array declaration char str[6] ; requests that space for 6 characters be set aside, to be known
by name str. In other words there is a location named str at which six characters are stored. The pointer declaration char *str ; on the other hand, requests a place that holds a pointer, to be known by the name str. This pointer can point almost anywhere to any char, to any contiguous array of chars, or nowhere.
How do I compare character data stored at two different memory locations?
Sometimes in a program we require to compare memory ranges containing strings. In such a situation we can use functions like memcmp( ) or memicmp( ). The basic difference between two functions is that memcmp( ) does a case-sensitive comparison whereas memicmp( ) ignores case of characters. Following program illustrates the use of both the functions.#include
main( )
{
char *arr1 = “Kicit” ;
char *arr2 = “kicitNagpur” ;
int c ;
c = memcmp ( arr1, arr2, sizeof ( arr1 ) ) ;
if ( c == 0 )
printf ( “\nStrings arr1 and arr2 compared using memcmp are identical” ) ;
else
printf ( “\nStrings arr1 and arr2 compared using memcmp are not identical”
) ;
c = memicmp ( arr1, arr2, sizeof ( arr1 ) ) ;
if ( c == 0 )
printf ( “\nStrings arr1 and arr2 compared using memicmp are identical” )
;
else
printf ( “\nStrings arr1 and arr2 compared using memicmp are not
identical” ) ;
}
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 < 160 ; offset++ )
fprintf ( fp, “%c”, peekb ( scr, offset ) ) ;
fclose ( fp ) ;
if ( ( fp = fopen ( “scr.dat”, “rb” ) ) == NULL )
{
printf ( “\nUnable to open file” ) ;
exit( ) ;
}
// reads and writes to file
for ( offset = 0 ; offset < 160 ; offset++ )
{
fscanf ( fp, “%c”, &ch ) ;
printf ( “%c”, ch ) ;
}
fclose ( fp ) ;
}
How do I write code to find an amount of free disk space available on current drive?
Use getdfree( ) function as shown in follow code.#include
#include
#include
#include
main( )
{
int dr ; struct dfree disk ;
long freesp ;
dr = getdisk( ) ;
getdfree ( dr + 1 , &disk ) ;
if ( disk.df_sclus == 0xFFFF )
{
printf ( “\ngetdfree( ) function failed\n”);
exit ( 1 ) ;
}
freesp = ( long ) disk.df_avail
* ( long ) disk.df_bsec
* ( long ) disk.df_sclus ;
printf ( “\nThe current drive %c: has %ld bytes
available as free space\n”, ‘A’ + dr, freesp ) ;
}
The functions memcmp( ) and memicmp( )
#include #include
main( )
{
char str1[] = “This string contains some
characters” ;
char str2[] = “this string contains” ;
int result ;
result = memcmp ( str1, str2, strlen ( str2 ) ) ;
printf ( “\nResult after comapring buffer using
memcmp( )” ) ;
show ( result ) ;
result = memicmp ( str1, str2, strlen ( str2 ) ) ;
printf ( “\nResult after comapring buffer using
memicmp( )” ) ;
show ( result ) ;
}
show ( int r )
{
if ( r == 0 )
printf ( “\nThe buffer str1 and str2 hold
identical data” ) ;
if ( r > 0 )
printf ( “\nThe buffer str1 is bigger than buffer
str2″ ) ;
if ( r < 0 )
printf ( “\nThe buffer str1 is less than buffer
str2″ ) ;
}
How do I write code to get the current drive as well as set the current drive?
The function getdisk( ) returns the drive number of current drive. The drive number 0 indicates ‘A’ as the current drive, 1 as ‘B’ and so on. The Setdisk( ) function sets the current drive. This function takes one argument which is an integer indicating the drive to be set. Following program demonstrates use of both the functions.#include
main( )
{
int dno, maxdr ;
dno = getdisk( ) ;
printf ( “\nThe current drive is: %c\n”, 65 + dno
) ;
maxdr = setdisk ( 3 ) ;
dno = getdisk( ) ;
printf ( “\nNow the current drive is: %c\n”, 65 +
dno ) ;
}
How do I write code that would get error number and display error message if any standard error occurs?
Following code demonstrates this.#include
#include
#include
main( )
{
char *errmsg ;
FILE *fp ;
fp = fopen ( “C:\file.txt”, “r” ) ;
if ( fp == NULL )
{
errmsg = strerror ( errno ) ;
printf ( “\n%s”, errmsg ) ;
}
}
Here, we are trying to open ‘file.txt’ file. However, if the file does not exist, then it would cause an error. As a result, a value (in this case 2) related to the error generated would get set in errno. errno is an external int variable declared in ’stdlib.h’ and also in ‘errno.h’. Next, we have called sterror( ) function which takes an error number and returns a pointer to standard error message related to the given error number.
How do I change the type of cursor and hide a cursor?
We can change the cursor type by using function _setcursortype( ). This function can change the cursor type to solid cursor and can even hide a cursor. Following code shows how to change the cursor type and hide cursor.#include
main( )
{
/* Hide cursor */
_setcursortype ( _NOCURSOR ) ;
/* Change cursor to a solid cursor */
_setcursortype ( _SOLIDCURSOR ) ;
/* Change back to the normal cursor */
_setcursortype ( _NORMALCURSOR ) ;
}
How do I write code to retrieve current date and time from the system and display it as a string?
Use time( ) function to get current date and time and then ctime( ) function to display it as a string. This is shown in following code snippet.#include
void main( )
{
time_t curtime ;
char ctm[50] ;
time ( &curtime ) ; //retrieves current time &
stores in curtime
printf ( “\nCurrent Date & Time: %s”, ctime (
&curtime ) ) ;
}
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] ;
}
Why doesn’t the following statement work?
char str[ ] = “Hello” ;strcat ( str, ‘!’ ) ;
Ans: 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, “!” ) ;
Why doesn’t the following code give the desired result?
int x = 3000, y = 2000 ;long int z = x * y ;
Ans: 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
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