View source for C Questions on Pointers ← C Questions on Pointers

<quiz display="simple">
{'''What will be the output of the following code?'''
<syntaxhighlight lang="c">
#include<stdio.h>

int main()
{
  int a = 5;
  int* p = &a;
  printf("%d", ++*p);
}
</syntaxhighlight>
|type="{}"
/}
{ 6 }
||p is pointing to the address of a. *p will return the content of a which is 5 and ++ will increment it to 6.


{'''What will be the output of the following code?'''
<syntaxhighlight lang="c">
#include<stdio.h>

int main()
{
  char a[] = "Hello World";
  char* p = &a;
  printf("%s", p+2 );
}
</syntaxhighlight>
|type="()"
/}
-Compiler Error
-World
+llo World
-Runtime Error

||Since p is a char pointer p+2 will add 2 to p (since sizeof(char) is 1). So, p+2 will be pointing to the string "llo World"

{'''What will be the output of the following code?'''
<syntaxhighlight lang="c">
#include<stdio.h>

int main()
{
  int a;
  int* p = &a;
  printf("%zu", sizeof( *(char*)p  ));
}
</syntaxhighlight>
|type="()"
/}

+1
-2
-4
-Compile Error

||p is typecasted to char pointer and then dereferenced. So, returned type will be char and sizeof(char) is 1

{'''Is the following code legal?'''
<syntaxhighlight lang="c">
#include<stdio.h>

int main()
{
  int a = 1;
  if((char*)  &a)
  {
    printf("My machine is little endian");
  }
  else
  {
     printf("My machine is big endian\n");
  }
}
</syntaxhighlight>
|type="()"
/}
+Yes
-No
||On a little endian machine the lower address will contain the least significant byte. Suppose a is stored at address 1000 and contains 1, then character at 1000 will be 1, if the machine is little endian


{'''Assuming a little endian machine, what will be the output of the following program?'''
<syntaxhighlight lang="c">
#include<stdio.h>

fun(int a)
{
  char *arr[] = {"0000", "0001","0010","0011","0100","0101","0110","0111","1000","1001","1010","1011","1100","1101","1110","1111"};
  unsigned char* p = (unsigned char*) &a ;
  p+=3;
  int i;
  for(i = 0; i < sizeof a; i++)
  {
    int d = (*p)>>4; 
    printf("%s", arr[d]);
    d = (*p) & 0xf;
    printf("%s ", arr[d]);
    p--;
  }
}

int main()
{
 int a;
 scanf("%d", &a);
 fun(a);
}
</syntaxhighlight>
|type="()"
/}
+Print the binary of the input number
-Compile error
-Runtime error
-Compiler dependent output
||The code is printing the binary equivalent of the input number. Suppose a is stored starting from address 1000. Since, we assume a little endian machine, the LSB of a will be stored at address 1000 and MSB will be stored at address 1003. So, we make a char pointer to 1003 and take out the MSB. Then using shift operator we get the most significant 4 bits from it and then the lest significant 4 bits. We repeat the same for the other three bytes of a. 
</quiz>