Difference between revisions of "C Questions on Pointers"

Revision as of 21:38, 15 June 2014

<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

{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 </quiz>

@@ Line 4: / Line 4: @@
 #include<stdio.h>
-int main(){
+int main()
+{
    int a = 5;
    int* p = &a;
    printf("%d", ++*p);
 }
 </syntaxhighlight>
@@ Line 21: / Line 21: @@
 #include<stdio.h>
-int main(){
+int main()
+{
    char a[] = "Hello World";
    char* p = &a;
    printf("%s", p+2 );
 }
 </syntaxhighlight>
@@ Line 41: / Line 41: @@
 #include<stdio.h>
-int main(){
+int main()
+{
    int a;
    int* p = &a;
    printf("%zu", sizeof( *(char*)p  ));
 }
 </syntaxhighlight>
@@ Line 58: / Line 58: @@
 ||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
+{'''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
 </quiz>