Difference between revisions of "C Coding Questions"

Revision as of 21:00, 19 May 2014 (view source) Arjun Suresh (talk | contribs) (→‎Data types) ← Older edit		Revision as of 21:03, 19 May 2014 (view source) Arjun Suresh (talk | contribs) (→‎Data types) Newer edit →
Line 1,092:		Line 1,092:
	+a = 4, b = 8		+a = 4, b = 8
		+
		+	{'''What will be the output of the following code?'''
		+	<syntaxhighlight lang="c">
		+
		+	#include <stdio.h>
		+	int main()
		+	{
		+	unsigned int a = 5;
		+	if(a > -1)
		+	printf("5 is > -1\n");
		+	return 0;
		+	}
		+	</syntaxhighlight>
		+	|type="()"
		+	/}
		+	||As explained in the chapter, when an operation involves different data types the lower ranked one is promoted to higher ranked one. So, when we compare a signed int with an unsigned int, the signed int will be promoted to unsigned (unsigned has higher rank than signed).
		+
		+	a > -1
		+	will turn to
		+	00...101 > 11...111
		+	and will evaluate to false
		+
		+	If a was declared as signed, then the if condition would have behaved as expected.
		+
		+	(Ideally an unsigned integer would never be compared with a negative number in real world and so do in programs)
		+
		+	-5 is > -1
		+	+No output
		+	-Compile Error
		+	-Runtime Error
	</quiz>		</quiz>

---

Revision as of 21:03, 19 May 2014

<quiz display="simple"> {What is the output of this program? <syntaxhighlight lang="c" >

1. include<stdio.h>

int main() {

   char *ptr;
   char string[] = "How are you?";
   ptr = string;
   ptr += 4;
   printf("%s",ptr);
   return 0;

} </syntaxhighlight> |type="()" /} -(a) How are you?

+(b) are you?

-(c) are

-(d) No output

{ Which of the following will print the value 2 for the above code? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a[10][20][30] = {0};
   a[5][2][1] = 2;

   return 0;

} </syntaxhighlight> |type="()" /} -(a) printf("%d",*(((a+5)+2)+1));

-(b) printf("%d",***((a+5)+2)+1);

+(c) printf("%d",*(*(*(a+5)+2)+1));

-(d) None of these

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 5;
   int b = ++a * a++;
   printf("%d ",b);
   return 0;

} </syntaxhighlight> |type="()" /} -(a)25

-(b) 30

-(c) 36

+(d) Undefined Behavior

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 5;
   switch(a)
   {
       default:
       a = 4;
       case 6:
           a--;
       case 5:
           a = a+1;
       case 1:
           a = a-1;
   }
   printf("%d \n",a);

   return 0;

} </syntaxhighlight> |type="()" /} +(a) 5

-(b) 4

-(c) 3

-(d) None of these

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 2,b = 5;
   a = a^b;
   b = b^a;
   printf("%d %d",a,b);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 5 2

-(b) 2 5

-(c) 7 7

+(d) 7 2

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

   int a[][3] = {1, 2, 3, 4, 5, 6};
   int (*ptr)[3] = a;
   printf("%d %d ", (*ptr)[1], (*ptr)[2]);
   ++ptr;
   printf("%d %d\n", (*ptr)[1], (*ptr)[2]);

   return 0;

} </syntaxhighlight> |type="()" /} +(a) 2 3 5 6

-(b) 2 3 4 5

-(c) 4 5 0 0

-(d) none of the above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

void f(char**);

int main() {

   char *argv[] = { "ab", "cd", "ef", "gh", "ij", "kl" };
   f(argv);

   return 0;

} void f(char **p) {

   char *t;
   t = (p += sizeof(int))[-1];
   printf("%s\n", t);

} </syntaxhighlight> |type="()" /} -(a) ab

-(b) cd

-(c) ef

+(d) gh

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdarg.h>
2. include <stdio.h>

int ripple(int n, ...) {

   int i, j, k;
   va_list p;
   k = 0;
   j = 0;
   va_start(p, n);
   for (; j < n; ++j)
   {
       i = va_arg(p, int);
       k += i;
   }
   va_end(p);
   
   return k;

} int main() {

   printf("%d\n", ripple(2, 5, 7));

   return 0;

} </syntaxhighlight> |type="()" /} +(a) 12

-(b) 5

-(c) 7

-(d) 15

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

int counter(int i) {

   static int count = 0;
   count = count + i;
   
   return count;

}

int main() {

   int i, j;
   for (i = 0; i <= 5; i++)
       j = counter(i);
   printf("%d\n", j);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 10

+(b) 15

-(c) 6

-(d) 7

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   const int x = 5;
   const int *ptrx;
   ptrx = &x;
   *ptrx = 10;
   printf("%d\n", x);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 5

-(b) 10

+(c) Compile Error

-(d) Garbage value

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. define x 4+1

int main() {

   int i;
   i = x*x*x;
   printf("%d",i);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 125

+(b) 13

-(c) 17

-(d) None of above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   char c=125;
   c=c+10;
   printf("%d",c);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 135

-(b) +INF

+(c) -121

-(d) -8

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int i=10;
   static int x=i;
   if(x==i)
       printf("Equal");
   else if(x>i)
       printf("Greater");
   else
       printf("Lesser");

   return 0;

} </syntaxhighlight> |type="()" /} -(a) Equal

-(b) Greater

-(c) Lesser

+(d) Compile Error

{Consider the following code segment: <syntaxhighlight lang="c">

1. include <stdlib.h>

int *f1() {

   int x = 10;
   return &x;

} int *f2() {

   int *ptr;
   *ptr = 10;
   return ptr;

} int *f3() {

   int *ptr;
   ptr = (int*) malloc(sizeof (*ptr));
   return ptr;

} </syntaxhighlight> Which of these functions uses pointers incorrectly? |type="()" /} +(a) f3 only

-(b) f1 and f3

-(c) f1 and f2

-(d) f1, f2, and f3

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

   int i = 3;
   int j;
   j = sizeof(++i + ++i);
   printf("i=%d j=%d\n", i, j);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) i=4 j=4

+(b) i=3 j=4

-(c) i=5 j=4

-(d) the behavior is undefined

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

void f1(int*, int); void f2(int*, int); void (*p[2])(int*, int);

int main() {

   int a = 3;
   int b = 5;
   p[0] = f1;
   p[1] = f2;
   p[0](&a, b);
   printf("%d %d ", a, b);
   p[1](&a, b);
   printf("%d %d\n", a, b);

   return 0;

}

void f1(int *p, int q) {

   int tmp = *p;
   *p = q;
   q = tmp;

} void f2(int *p, int q) {

   int tmp = *p;
   *p = q;
   q = tmp;

} </syntaxhighlight> |type="()" /} +(a) 5 5 5 5

-(b) 3 5 3 5

-(c) 5 3 3 5

-(d) none of the above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

void e(int);

int main() {

   int a = 3; 
   e(a);
   putchar('\n');

   return 0;

} void e(int n) {

   if (n > 0)
   {
       e(--n);
       printf("%d ", n);
       e(--n);
   }

} </syntaxhighlight> |type="()" /} +(a)0 1 2 0

-(b) 0 1 2 1

-(c) 1 2 0 1

-(d) 0 2 1 1

{ Consider the following code segment: <syntaxhighlight lang="c"> typedef int (*test)(float*, float*); test tmp; </syntaxhighlight> What is the type of tmp? |type="()"

/} -(a) function taking two pointer-to-float arguments and returning pointer to int

-(b) pointer to int

+(c) pointer to function taking two pointer-to-float arguments and returning int

-(d) none of the above

{ What is the output of the following program?' <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

   char p;
   char buf[10] = {1, 2, 3, 4, 5, 6, 9, 8};
   p = (buf + 1)[5];
   printf("%d\n", p);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 5

-(b) 6

+(c) 9

-(d) none of the above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

   struct node
   {
       int a;
       int b;
       int c;
   };
   struct node s = { 3, 5, 6 };
   struct node *pt = &s;
   printf("%d\n", *((int*)pt+1));

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 3

+(b) 5

-(c) 6

-(d) 7

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

int main(void) {

   char a[5] = { 1, 2, 3, 4, 5 };
   char *ptr = (char*)(&a + 1);
   printf("%d %d\n", *(a + 1), *(ptr - 1));

   return 0;

} </syntaxhighlight> |type="()" /} -(a) Compile Error

-(b) 2 1

+(c) 2 5

-(d) none of the above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>

void foo(int[][3]);

int main(void) {

   int a[3][3] = { {1, 2, 3}, {4, 5, 6}, {7, 8, 9} };
   foo(a);
   printf("%d\n", a[2][1]);

   return 0;

}

void foo(int b[][3]) {

   ++b;
   b[1][1] = 9;

} </syntaxhighlight> |type="()" /} -(a) 8

+(b) 9

-(c) 7

-(d) none of the above

{Consider the following function: <syntaxhighlight lang="c"> int foo(int x, int n) {

   int val = 1;
   if (n > 0)
   {
       if (n % 2 == 1)
       val *= x;
       val *= foo(x * x, n / 2);
   }
   return val;

} </syntaxhighlight>

What function of x and n is computed by foo? |type="()" /} +(a) $x^n$

-(b) $x×n$

-(c) $n^x$

-(d) none of the above

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 0;
   switch(a)
   {
       default:
           a = 4;
       case 6:
           a--;
       case 5:
           a = a+1;
       case 1:
           a = a-1;
   }
   printf("%d \n",a);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) 5

-(b) 4

+(c) 3

-(d) 0

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 2;
   if(a == (1,2))
       printf("Hello");
   if(a == 1,2)
       printf("World");

   return 0;

} </syntaxhighlight> |type="()" /} -(a) Hello

-(b) World

+(c) HelloWorld

-(d) Compile Error

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a = 1,2;
   int b = (1,2);
   if(a == b)
       printf("Equal");
   else
       printf("Not Equal");

   return 0;

} </syntaxhighlight> |type="()" /} -(a) Equal

-(b) Not Equal

-(c) Compiler Dependent

+(d) Compile Error

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

void foo(char *);

int main() {

   char *string = "Hello";
   foo(string);
   printf("%s",string);

   return 0;

}

void foo(char *a) {

   while(*a)
   {
       *a += 1;
       a++;
   }

} </syntaxhighlight> |type="()" /} -(a) Hello

-(b) Ifmmp

-(c) Compile Error

+(d) Segmentation fault

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. include<stdlib.h>

int main() {

   char s[] = "Hello World";
   int i = 0;
   while(*(s++))
       i++;
   printf("%d",i);

   return 0;

} </syntaxhighlight> |type="()" /} -(a) Segmentation Fault

+(b) Compile Error

-(c) 12

-(d) 0

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int a = 10; int main() {

   fun();
   fun();

   return 0;

}

int fun() {

   static int a = 1;
   printf("%d ",a);
   a++;

   return 0;

} </syntaxhighlight> |type="()" /} +(a) 1 2

-(b) 1 1

-(c) 10 11

-(d) 10 10

{What is the output of the following program? <syntaxhighlight lang="c">

1. include <stdio.h>
2. define crypt(s,t,u,m,p,e,d) m##s##u##t
3. define begin crypt(a,n,i,m,a,t,e)

int begin() {

   printf("Hello\n");

   return 0;

} </syntaxhighlight> |type="()" /} +(a) Hello

-(b) Link error

-(c) Segmentation fault

-(d) Compiler error

{Consider the following program: <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a[10][20][30]={0};
   printf("%ld",&a+1 - &a);

   return 0;

} </syntaxhighlight> What is the output of this program? |type="{}" /} { 1 }

{Consider the following program: <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a[10][20][30] = {0};
   int *b = a;
   int *c = a+1;
   printf("%ld", c-b);

   return 0;

} </syntaxhighlight> What is the output of this program? (You may ignore compiler warnings) |type="{}" /} { 600 }

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. include<stdlib.h>

int* fun();

int main() {

   int *a = fun();
   printf("%d",*a);

   return 0;

} int* fun() {

   int *a =(int*) malloc(sizeof(int));
   *a = 10;
   return a;

} </syntaxhighlight> |type="{}" /} { 10 }

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int *a = fun();
   printf("%d",a);

   return 0;

} int fun() {

   int a = 10;
   return a;

} </syntaxhighlight> |type="{}" /} { 10 }

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. include<string.h>

int main() {

   char string[] = "Hello";
   printf("%zu %zu",sizeof(string),strlen(string));

   return 0;

} </syntaxhighlight> |type="{}" /} { 6 5 }

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   float a = 0.5;
   if(a == 0.5)
       printf("Yes");
   else
       printf("No");

   return 0;

} </syntaxhighlight> |type="{}" /} { Yes }

{What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. include<string.h>

void foo(char *);

int main() {

   char a[100] = {0};
   printf("%zu %zu",sizeof(a),strlen(a));

   return 0;

} </syntaxhighlight> |type="{}" /} { 100 0 }

{What is the output of the following program? (Assume input is 10) <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   int a;
   printf("%d",scanf("%d",&a));

   return 0;

} </syntaxhighlight> |type="{}" /} { 1 }

{If the binary equivalent of 5.375 in normalised form is 0100 0000 1010 1100 0000 0000 0000 0000, what will be the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>
2. include<math.h>

int main() {

   float a=5.375;
   char *p;
   int i;
   p = (char*)&a;
   for(i=0; i<2; i++)
       printf("%x", (unsigned char)(p[i]^p[3-i]));

   return 0;

} </syntaxhighlight> |type="{}" /} { 40ac }

{ What is the output of the following program? <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   char str[] = {'a','b','c','\0'};
   str[0] -= 32;
   printf("%s",str);

   return 0;

} </syntaxhighlight> |type="{}" /} { Abc }

</quiz>

Data types

<quiz display="simple"> {Consider an implementation where int is 4 bytes and long int is 8 bytes. Which of the following initializations are correct? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

  long int a = 0x7fffffff * 0x7ffffff;
  long int b = 0x7ffffffff * 0x7ffffff;
  long int c = 0x7fffffff * 0x7fffffff;
  long int d = 0x7fffffff * 0x7fffffffl;
  printf("a = %ld, b = %ld, c = %ld, d = %ld\n", a, b, c, d);
  return 0;

} </syntaxhighlight> |type="()" /} -All are correct -a, c, d +b, d -a, d ||a and c choices cause integer overflow. Even though long int can hold 8 bytes as given in the question, the operands are of 4 bytes only and hence the result is also 4 bytes.

||In b choice, 0x7ffffffff is taking more than 4 bytes and hence is considered a long int. So, the next operand is implicitly typecasted to long int and the result is also calculated as long int. Hence there'll be no overflow.

||In d choice, by adding l at the end, we force the compiler to use long int operand and hence the operations will be done using 8 byte operands and there will be no overflow.

{Consider an implementation where int is 4 bytes and long int is 8 bytes. What will be the output of the following code? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

  int i = 0;
  size_t a = sizeof i, b = sizeof (long);
  printf("a = %zd, b = %zd\n", a, b); //If %zd is given the compiler will automatically give it the correct type whether short, long or normal. This is useful for special data types like size_t whose size is implementation specific
  return 0;

} </syntaxhighlight> |type="()" /} ||sizeof is an operator and hence we don't need a parentheses for giving variables to sizeof. So, sizeof i will return 4 which is the size of int and sizeof(long) will return 8 -Compile error -Runtime error -a = 4, b = 4 +a = 4, b = 8

{What will be the output of the following code? <syntaxhighlight lang="c">

1. include <stdio.h>

int main() {

  unsigned int a = 5;
  if(a > -1)
     printf("5 is > -1\n");
  return 0;

} </syntaxhighlight> |type="()" /} ||As explained in the chapter, when an operation involves different data types the lower ranked one is promoted to higher ranked one. So, when we compare a signed int with an unsigned int, the signed int will be promoted to unsigned (unsigned has higher rank than signed).

a > -1 will turn to 00...101 > 11...111 and will evaluate to false

If a was declared as signed, then the if condition would have behaved as expected.

(Ideally an unsigned integer would never be compared with a negative number in real world and so do in programs)

-5 is > -1 +No output -Compile Error -Runtime Error </quiz>

Some codes

1. What is the following function doing? <syntaxhighlight lang="c"> int foo(int n) {

   int sum = 0;
   while(n > 0)
   {
       n = n & n-1;
       sum++;
   }
   return sum;

} </syntaxhighlight> Ans:

2. What is the following function doing? <syntaxhighlight lang="c"> int foo(int a, int b) {

   int c = a, d = b;
   while(a != b)
   {
       if(a < b)
           a = a+c;
       else
           b = b+d;
   }
   return a;

} </syntaxhighlight> Ans:

3. What is the following function doing? <syntaxhighlight lang="c"> int foo( int a, int b) {

   int c = a-b;
   c = c&(0x80000000);
   return (!c)*a +(!!c)*b;

} </syntaxhighlight> Ans:

4. What is the following function doing? <syntaxhighlight lang="c"> unsigned fun(unsigned a, unsigned b) {

   int i;
   unsigned  j = 0;
   for(i = 0; i < 32; i++)
   {
       j <<= 1;
       j += !!(a & 0x80000000);
       a <<= 1;
       if(j >=b)
       {
           j -= b;
           a++;
       }
   }
   return a;

} </syntaxhighlight> Ans:

5. What is the following function doing? <syntaxhighlight lang="c"> unsigned fun(unsigned int a) {

   unsigned int i, x = 0, y = 0, z = 0;
   for(i = 0; i < 16; i++)
   {
      	y <<= 2;
      	y += !!(a & 0x80000000) << 1;
      	y += !!(a & 0x40000000);
      	a <<= 2;
      	x = x + (x&1);
      	x <<= 1;
      	z <<= 1;
      	if(x + 1 <= y)
      	{
           x++;
           z++;

y-=x;

       }
   }
   return z;

} </syntaxhighlight> Ans:

6. Write the code to dynamically allocate a 2-D array of size m x n.

Ans:

7. Declare a pointer to a function accepting an integer and returning void.

Ans:

8. Write the condition so that the below code outputs <math>\unicode{x201C}</math>Hello World<math>\unicode{x201D}</math>. <syntaxhighlight lang="c">

1. include<stdio.h>

int main() {

   if(<condition>)
   {

printf("Hello ");

   }
   else
   {

printf("World\n");

   }

   return 0;

} </syntaxhighlight> Ans:

9. Write a one line code to check if a number is a power of 2.

Ans:

10. Write a one line code to invert the last four bits of an integer.

Ans: