C Aptitude Questions with Answers Part 2

1.

main(){ 
   extern int i; 
   i=20; 
   printf("%d",i); 
} 

Answer:
Linker Error : Undefined symbol '_i' 
Explanation:   extern storage class in the following declaration, extern int i; specifies to the compiler that the memory for i is allocated in some other program and that address will be given to the current program at the time of linking. But linker finds that no other variable of name i is available in any other program with memory space allocated for it. Hence a linker error has occurred .

2.

main(){
   int i=-1,j=-1,k=0,l=2,m; 
   m=i++&&j++&&k++||l++; 
   printf("%d %d %d %d %d",i,j,k,l,m); 
} 

Answer: 0 0 1 3 1
Explanation :  Logical operations always give a result of 1 or 0 . And also the logical AND (&&) operator has higher priority over the logical OR (||) operator. So the expression ‘i++ && j++ && k++’ is executed first. The result of this expression is 0 (-1 && -1 && 0 = 0). Now the expression is 0 || 2 which evaluates to 1 (because OR operator always gives 1 except for ‘0 || 0’ combination- for which it gives 0). So the value of m is 1. The values of other variables are also incremented by 1.

3.

main(){ 
   char *p; 
   printf("%d %d ",sizeof(*p),sizeof(p)); 
} 

Answer: 1 2
Explanation:  The sizeof() operator gives the number of bytes taken by its operand. P is a character pointer, which needs one byte for storing its value (a character). Hence sizeof(*p) gives a value of 1. Since it needs two bytes to store the address of the character pointer sizeof(p) gives 2.

4.

   main(){
  int i=3; 
  switch(i) 
   { 
      default:printf("zero"); 
      case 1: printf("one"); 
       break; 
     case 2:printf("two"); 
      break; 
    case 3: printf("three"); 
      break; 
    }   
} 

Answer :
three 

Explanation :  The default case can be placed anywhere inside the loop. It is executed only when all other cases doesn't match.

5.

 main(){ 
    printf("%x",-1<<4); 
} 

Answer:
fff0 
Explanation :  -1 is internally represented as all 1's. When left shifted four times the least significant 4 bits are filled with 0's.The %x format specifier specifies that the integer value be printed as a hexadecimal value.