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Friday, August 27, 2010

Chapter-7 Pointers

CHAPTER-7

                        POINTERS



1.Can you combine the following two statements into one
char *p;
p=malloc(100);

Ans: char *p=malloc(100);
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2.Can you split the following statement into two statements?
Char far *scr=(char far*) 0xb8000000L;

Ans:
Char far *scr;
Scr=(char far*) 0xb8000000L;
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3.Are the expressions *ptr++ and ++*ptr same?

Ans: No. *ptr++ increments the pointer and not the value pointed by it, whereas ++*ptr increments the value being pointed to by ptr.
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4. Can You write another expression which does the same job as ++*ptr?


Ans:  (*ptr)++

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5.What would be the equivalent pointer expression for referring the same element as a[i][j][k][l]?


Ans:   *(*(*(*(a+i)+j)+k)+l)
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6.O/p?
main()
{
  int arr[]=(12,13,14,15,16};
  printf(“\n%d %d %d”,sizeof(arr),sizeof(*arr),sizeof(arr[0]));
}


Ans: 10 2 2

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7.What would be the O/P of the program assuming that the array begins at 1002?
Main()
{
  int a[3][4]={
                       1,2,3,4,
                       5,6,7,8,
                       9,10,11,12
                   };
     printf(“\n%u %u %u”,a[0]+1,*(a[0]+1),*(*(a+0)+1));
}


Ans: 1004 2 2

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8.What would be the output of the program assuming that the array begins at location 1002?
Main()
{
  int a[2][3][4]={
                           {
                               1,2,3,4,
                               5,6,7,8,
                               9,1,1,2
                           },
                          {
                              2,1,4,7,
                              6,7,8,9,
                              0,0,0,0
                          }
                      }
 printf(“\n %u  %u  %u  %d”,a,*a,**a,***a);


Ans:1002  1002  1002  1

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9.In the following program how would you print 50 using p?
main()
{
  int a[]={10,20,30,40,50}
  char *p;
  p=(char*)a;
}

 Ans: printf(“\n %d”,*((int*)p+4));
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10.Where can one think of using pointers?


Ans: At lot of places,for eg
 Accessing array or string elements
 Dynamic memory allocation
 Call by referance
 Implementing linked lists, trees, graphs, and many other data structures
 Etc.
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11.In the following program add a statement in the function fun() such that the address of  a  gets stored in j.
main()
{
  int *j;
  void fun(int**);
  fun(&j);
}
void fun(int**k)
{
  int a=10;
 /* add statement here*/
}


Ans:  *k=&a;
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12.How would you implement an array of three function pointers where each function receives two ints and return a float?


Ans: float (*arr[3])(int,int);
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13. Would the following program give a compilation error or warning?
main()
{
  float i=10,*j;
  void *k;
  k=&i;
  j=k;
  printf(“\n%f”,*j);
}



Ans: No. Hee no type casting is required while assigning the value to and from k because conversions are applied automatically when other pointer types are assigned to and from void*.
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14. Would the following program compile?
main()
{
  int a=10,*j;
  void *k;
  j=k=&a;
  j++;
  k++;
  printf(“\n %u  %u”,j,k);
}



Ans: No. An error would be reported in the statement k++ since arithmetic on void pointers is not permitted unless the void pointer is appropriately typecasted.
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15. Would the following code compile successfully?
main()
{
  printf(“%c”,7[“Sundaram”]);
}



Ans: YES. Prints m of sundaram.
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Friday, August 20, 2010

Chapter-6 The C-Preprocessor

CHAP  6


            THE  C  PREPROCESSOR



1.               If a file to be included doesn’t exist, the preprocessor flashes an error message.


Ans: TRUE.
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2.            The preprocessor can trap simple errors like missing declarations, nested comments or mismatch of braces.


Ans: FALSE.
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3.            O/p?
#define SQR(x) (x * x)
 main()
 {
  int a,b=3;
  a=SQR(b+2);
  printf(“\n%d”,a);
 }
a.                         25
b.                        11
c.                         error
d.                        garbage value


ans:B. Because on preprocessing the expression becomes (3+2 * 2+3).
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4.How would you define SQR macro above in Q3 such as it gives the result of a as 25


ans: #SQR(x) ((x) * (x))
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5.            O/p?
#define CUBE(x) (x * x * x)
 main()
{
 int a,b=3;
 a=CUBE(b++);
 printf(“\n %d %d”,a,b);
 }


Ans: 27 6. Though some compilers may give this as an answer, according to ANSI C the expression b++ * b++ * b++ is undefined. Refer to chap 3 for more details.
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6.Indicate what the SWAP macro be expanded to on preprocessing. Would the code compile?

#define SWAP(a,b,c) (c t; t=a, a=b, b=t;)
main()
{
 int x=10,y=20;
 SWAP(x,y,int);
 Printf(“%d %d”,x,y);
}


Ans: (int t; t=a, a=b, b=t;);
This code won’t compile since the declaration of t can’t take place within parenthesis.
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7.            How should you modify SWAP macro such that it can swap two integers?


Ans: #define SWAP(a,b,c)  c t; t=a, a=b, b=t;
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8.What is the limitation of SWAP macro above In Q7?


Ans: It can’t swap pointer’s for example the following code won’t compile:-
#define SWAP(a,b,c)  c t; t=a, a=b, b=t;
main()
{
 float x=10,y=20;
 float p,q;
 p=&x;  q=&y;
 SWAP(p, q, float);
 Printf(“%f %f”, x, y);
}


9.In which line of the following program, the error would be reported?

1               #define CIRCUM® (3.14 * r* r);
2               main()
3               {
4                 float r=1.0.c;
5                 c=CIRCUM(r);
6                 printf(“\n %f”,c);
7                 if(CIRCUM(r) == 6.28)
8                    printf(“\n Good Day!”);
9                }


Ans: Line number 7. Whereas the culprit is really the semicolon in line 1. )n expansion line no 7 becomes   if((3.14 * 1.0 *1.0);== 6.28). Hence the error.
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10.What is the type of variable b in the following declaration?

#define FLOATPTR float *
FLOATPTR a,b;


Ans: FLOAT. Since on expansion declaration becomes    float *a,b;

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11.Is it necessary that the header files should have a .h extension?


Ans: NO.
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12. What do the header files usually contain?

Ans: Preprocessor directives like #define, structure,union, and enum declarations, typedef declarations, global variable declarations and external function declarations. You should not write the actual code (function bodies) or global variable definition (that is defining or initializing instances) in header files. The #include directive should be used to pull in header files, not other .c files.
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13.Would it result into an error if a header file is included twice?


Ans: YES. Unless the header file has taken care to ensure that if already included it doesn’t get included again.
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14.How can a header file ensure that it doesn’t get included more than once?


Ans:  All declarations must be written in a manner shown bellow. Assume that the name of the header file is FUNCS.H.

/* FUNCS.H */
#ifndef _FUNCS
   #define _FUNCS
      /* all declarations would go here */
#endif
Now if we include this file twice as shown bellow, it would get included only once
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15.On inclusion, where are the header files searched for?


Ans: If included using < > the files get searched in the predefined (can be changed) include path. If included using “ “ syntax in addition to the predefined include path the files also get searched in the current directory (usually the directory from which you invoke the comlier).
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16.Would the following #typedef work?
typedef  #include l;


Ans: NO. Because typedef goes to work after preprocessing.
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17. Would the following code compile correctily?
main()
{
  #ifdef NOTE
     /* unterminated comment
     int a;
     a=10;
 #else
   int a;
   a=20;
 #endif

  printf(“%d”,a);
}


Ans: NO. Even though #ifdef fails in this case (NOTE being undefined) and the if block doesn’t go for compilation errors in it are not permitted.
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18. O/p?
#define MESS junk
main()
{
   printf(“MESS”);
}


Ans: MESS

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19. Will the following program print the message infinite times?
#define INFINITELOOP while(1)
main()
{
   INFINITELOOP
      Printf(“\n HELLOW”);
}


Ans: :YES.
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20.O/p?
#define MAX(a,b) (a>b?a:b)
main()
{
   int x;
   x=MAX(3+2,2+7);
   printf(“%d”,x);
}


Ans: 9

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21. O/p?
#define PRINT(int) printf(“%d”,int)
main()
{
 int x=2,y=3,z=4;
 PRINT(x);
 PRINT(y);
 PRINT(z);
}

Ans: 2 3 4

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22.O/P?
#define PRINT(int) printf(“int=%d”,int)
main()
{
  int x=2,y=3,z=4;
  PRINT(x);
  PRINT(y);
  PRINT(z);
}


Ans: int=2 int=3 int=4

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23.How would modify the macro of Q22 above such that it outputs
x=2 y=3 z=4


Ans:
#define PRINT(int) printf(#int”=%d”,int)
main()
{
  int x=2, y=3, z=4;
 PRINT(x);
 PRINT(y);
 PRINT(z);
}
The rule is if the parameter name is preceded by a # in the macro expansion, the combination (of # and parameter) will be expanded into a quoted string with the parameter replaced by the actual argument. This can be combined with string concatenation to print the output desired in our program. On expansion the macro becomes
Printf(“x” “=%d”,x);
The two strings get concatenated, so the effect is
Printf(“x=%d”,x);

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24.Would the following program compile successively?
main()
{
    printf(“Tips” ”Traps”);
}


Ans: Yes. The o/p is TipsTraps.
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25. Define the macro DEBUG such that the following program outputs:
DEBUG: x=4;
DEBUG: y=3.140000
DEBUG: ch=A

main()
{
  int x=4;
  float y=3.14;
  char ch=’A’;
  DEBUG (x,”%d”);
  DEBUG (a,”%f”);
  DEBUG (ch,”%c”);
}


Ans: #define DEBUG(var, Fmt) printf(“DEBUG:” #var ”=” #fmt ”\n”,ar)
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26.O/p?
#define str(x) #x
#define Xstr(x) str(x)
#define oper multiply
main()
{
   char *opername=Xstr(oper);
   printf(“%s”,opername);
}


Ans: multiply

Here the two operations are being carried out expansion and stringizing. Xstr() macro expands its argument, and then str() stringizes it.
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27. Write the macro PRINT for the following program such that it outputs:
x=4 y=4 z=5
a=1 b=2 c=3
main()
{
  int x=4, y=4, z=5;
  int a=1, b=2, c=3;
  PRINT(x,y,z);
  PRINT(a,b,c);
}

Ans: #define PRINT(var1, var2, var3) printf(“\n” #var1 “=%d”#var2 “=%d” #var3 “=%d”, var1,var2,var3)
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Chapter-5 Functions




Chapter- 5     FUNCTIONS

1.O/p?
main()
{
  int a,b;
  a=sumdig(123);
  b=sumdig(123);
  printf(“%d %d”,a,b);
}

sumdig(int n)
{
  static int s=0;
  int d;
  if(n!=0)
  {
  d=n%10;
  n=(n-d)/10;
  s=s+d;
  sumdig();
  }
 else
    return(s);
}


ans: 6 12;
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2.What error would the following function give on compilation.
F(int a,int b)
{
 int a;
 a=20;
return a;
}

A.missing parenthesis in return statement.
B.The function should be defined as   int f(int a,int b)
C.Redeclaratin of a.
     D. None of above.

Ans: C.
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3.Thee is a mistake in the following code. Add a statement in it to remove it.
Main()
{
 int a;
 a=f(10,3.14);
 printf(“%d”,a);
}

f(int aa,float bb)
{
 return((float(aa)+bb);
}


ans: Add the following function prototype in main()
  float f(int aa,float bb);
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4. Point error in the following code.
Main()
{
 int a=10;
 void f();
 a=f();
 printf(“%d”,a);
}

void f()
{
 printf(“HI”);
}

ans. In spite of decelerating that the function will return void the program is trying to collect the value in a variable.
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5.Point error if any
main()
{
 int b;
 b=f(20);
 printf(“%d”,b);
 }

int f(int a)
{
  a>20?return(10):return(20);
}


ans: Return statement can not be used in format as shown in the conditional operator instead it should be as follows
   return(a>20?10:20);
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6. A function can not be defined inside another function.

ans: True.
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7.Will the following function work?
f1(int a, int b)
{
   return(f2(20));
}

f2(int a)
{
 return(a*a);
}

ans:YES.
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8.What are following two notations of defining functions commonly known as
 int f(int a, float b)
{
  /* some code */
}

int f(a,b)
int a, float b;
{
  /* some code */
}

ans: The first one is known as ANSI notation. And the second one is known as Kernighan and Ritche, or simply K & R notation
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9.In function two return statements should not occuar.

ans: FALSE.
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10. In a function two return statements should not occur successively.


ans: TRUE.
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11.In C all functions except main() can be called recursively.


Ans:FALSE. Any function including main() can be called recursively.
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12. Usually recursion works slower than loops.


ans: TRUE.
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13.Is it true that too many recursive calls may result in stack overflow?


Ans TRUE.
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14. How many times the following program prints ‘Jambaree’?
main()
{
 printf(“\n Jambaree”);
main();
}
a.       infinite.
b.      32767 times
c.       65535 times
d.      Till stack doesn’t overflow.


Ans: D
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