C Coding Questions

Consider the following program:

#include <stdio.h> int main() { int a[10][20][30]={0}; printf("%ld",&a+1 - &a); return 0; }

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#include <stdio.h>
int main()
{
    int a[10][20][30]={0};
    printf("%ld",&a+1 - &a);

    return 0;
}

What is the output of this program?

Consider the following program:

#include <stdio.h> 
int main()
{
    int a[10][20][30] = {0};
    int *b = a;
    int *c = a+1;
    printf("%ld", c-b);
 
    return 0;
}
What is the output of this program? (You may ignore compiler warnings)

#include <stdio.h>

int main()

{

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

int *b = a;

int *c = a+1;

printf("%ld", c-b);

return 0;

}

What is the output of this program? (You may ignore compiler warnings)

What is the output of the following program?

#include <stdio.h>
#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;
}

#include <stdio.h>

#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;

}

What is the output of the following program?

#include <stdio.h> int main() { int *a = fun(); printf("%d",a); return 0; } int fun() { int a = 10; return a; }

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#include <stdio.h>
int main()
{
    int *a = fun();
    printf("%d",a);

    return 0;
}
int fun()
{
    int a = 10;
    return a;
}
What is the output of the following program?

#include <stdio.h> #include <string.h> int main() { char string[] = "Hello"; printf("%zu %zu",sizeof(string),strlen(string)); return 0; }

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#include <stdio.h>
#include <string.h>

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

    return 0;
}
What is the output of the following program?

#include <stdio.h> int main() { float a = 0.5; if(a == 0.5) printf("Yes"); else printf("No"); return 0; }

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#include <stdio.h>
int main()
{
    float a = 0.5;
    if(a == 0.5)
        printf("Yes");
    else
        printf("No");

    return 0;
}
What is the output of the following program?

#include <stdio.h> #include <string.h> void foo(char *); int main() { char a[100] = {0}; printf("%zu %zu",sizeof(a),strlen(a)); return 0; }

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#include <stdio.h>
#include <string.h>
void foo(char *);

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

    return 0;
}
What is the output of the following program? (Assume input is 10)

#include <stdio.h> int main() { int a; printf("%d",scanf("%d",&a)); return 0; }

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#include <stdio.h>
int main()
{
    int a;
    printf("%d",scanf("%d",&a));

    return 0;
}

If the binary equivalent of 5.375 in normalised form is 01000000 10101100 00000000 00000000, what will be the output of the following program?

#include <stdio.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;
}

#include <stdio.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;

}

What is the output of the following program?

#include <stdio.h> int main() { char str[] = {'a','b','c','\0'}; str[0] -= 32; printf("%s",str); return 0; }

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#include <stdio.h>
int main()
{
    char str[] = {'a','b','c','\0'};
    str[0] -= 32;
    printf("%s",str);

    return 0;
}

Questions from Datatypes

Consider an implementation where int is 4 bytes and long int is 8 bytes. Which of the following initializations are correct?

#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;
}

#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;

}

Consider an implementation where int is 4 bytes and long int is 8 bytes. What will be the output of the following code?

#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;
}

#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;

}

What will be the output of the following code?

#include <stdio.h> int main() { unsigned int a = 5; if(a > -1) printf("5 is > -1\n"); return 0; }

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#include <stdio.h>
int main()
{
   unsigned int a = 5;
   if(a > -1)
      printf("5 is > -1\n");
   return 0;
}
What will be printed by the following code?

#include <stdio.h> int main() { char buff[255] = "abc\ pee"; printf("%s", buff); return 0; }

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#include <stdio.h>

int main()
{
   char buff[255] = "abc\
pee";
   printf("%s", buff);
   return 0;
}
What will be printed by the following code?

#include <stdio.h> int main() { char buff[255] = "\0"; printf("%s", buff); return 0; }

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#include <stdio.h>

int main()
{
    char buff[255] = "\0";
    printf("%s", buff);
    return 0;
}

What will be the output of the following code? (Assume a 64 bit machine/compiler)

#include <stdio.h>
int main()
{
    char *p = "Hello World";
    char q[] = "Hello World";
    printf("%zd %zd", sizeof p, sizeof *p);
    printf("\n");
    printf("%zd %zd", sizeof q, sizeof *q);
    return 0;
}

#include <stdio.h>

int main()

{

char *p = "Hello World";

char q[] = "Hello World";

printf("%zd %zd", sizeof p, sizeof *p);

printf("\n");

printf("%zd %zd", sizeof q, sizeof *q);

return 0;

}

What will be the output of the following code?

#include <stdio.h>
int main()
{
   {
      char a = 5;
      int b = 5;
      if(a == b)          
         printf("char and int compared equal\n");    }
   {
      int a = 5;
      long int b = 5;
if(a == b)
         printf("int and long compared equal\n");
   }
   {
      float a = 5.0;
      double b = 5.0;
      if(a == b)
         printf("float and double compared equal\n");
   }
   {
      float a = 5.2;
      double b = 5.2;
      if(a == b)
         printf("float and double again compared equal\n");
   }
   {
      float a = 5.2;
      if(a == 5.2)
         printf("float compared equal with constant\n");
   }
   {
      double a = 5.2;
      if(a == 5.2)
         printf("double compared equal with constant\n");
   }
   return 0;
}

#include <stdio.h>

int main()

{

char a = 5;

int b = 5;

if(a == b)

printf("char and int compared equal\n"); }

{

int a = 5;

long int b = 5;

if(a == b)

printf("int and long compared equal\n");

}

{

float a = 5.0;

double b = 5.0;

if(a == b)

printf("float and double compared equal\n");

}

{

float a = 5.2;

double b = 5.2;

if(a == b)

printf("float and double again compared equal\n");

}

{

float a = 5.2;

if(a == 5.2)

printf("float compared equal with constant\n");

}

{

double a = 5.2;

if(a == 5.2)

printf("double compared equal with constant\n");

}

return 0;

}

Questions from Pointers

What will be the output of the following code?

#include <stdio.h> int main() { int a = 5; int* p = &a; printf("%d", ++*p); }

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#include <stdio.h>

int main()
{
  int a = 5;
  int* p = &a;
  printf("%d", ++*p);
}
What will be the output of the following code?

#include <stdio.h> int main() { char a[] = "Hello World"; char* p = &a; printf("%s", p+2 ); }

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#include <stdio.h>

int main()
{
  char a[] = "Hello World";
  char* p = &a;
  printf("%s", p+2 );
}
What will be the output of the following code?

#include <stdio.h> int main() { int a; int* p = &a; printf("%zu", sizeof( *(char*)p )); }

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#include <stdio.h>

int main()
{
  int a;
  int* p = &a;
  printf("%zu", sizeof( *(char*)p  ));
}

Is the following code legal?

#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");
  }
}

#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");

}

What will be the output of the following code?

#include <stdio.h> int main() { int *a = (int*) 1; printf("%d", a); }

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#include <stdio.h>

int main()
{
int *a = (int*) 1;
printf("%d", a);
}
What will be the output of the following code?

#include <stdio.h> int main() { int a = 1, *p, **pp; p = &a; pp = p; printf("%d", **pp); }

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#include <stdio.h>

int main()
{
  int a = 1, *p, **pp;
  p = &a;
  pp = p;
  printf("%d", **pp);
}
What will be the output of the following code?

#include <stdio.h> int main() { int a = 1, *p, **pp; p = &a; pp = p; printf("%d", *pp); }

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#include <stdio.h>

int main()
{
  int a = 1, *p, **pp;
  p = &a;
  pp = p;
  printf("%d", *pp);
}

Assuming a little endian machine, what will be the output of the following program?

#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);
}

#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);

}

Some codes

What is the following function doing?

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

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

What is the following function doing?

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

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;

}

What is the following function doing?

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

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

What is the following function doing?

unsigned fun(unsigned a, unsigned b)
{
    int i;
    unsigned  j = 0;
    for(i = 0; i &lt; 32; i++)
    {
        j &lt;&lt;= 1;
        j += !!(a &amp; 0x80000000);
        a &lt;&lt;= 1; if(j &gt;=b)
        {
            j -= b;
            a++;
        }
    }
    return a;
}

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;

}

What is the following function doing?

unsigned fun(unsigned int a)
{
    unsigned int i, x = 0, y = 0, z = 0;
    for(i = 0; i &lt; 16; i++)
    {
       	y &lt;&lt;= 2;
       	y += !!(a &amp; 0x80000000) &lt;&lt; 1;
       	y += !!(a &amp; 0x40000000);
       	a &lt;&lt;= 2;
       	x = x + (x&amp;1);
       	x &lt;&lt;= 1;
       	z &lt;&lt;= 1;
       	if(x + 1 &lt;= y)
       	{
            x++;
            z++;
	    y-=x;
        }
    }
    return z;
}

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;

}

Write the code to dynamically allocate a 2-D array of size m x n.
Declare a pointer to a function accepting an integer and returning void.
Write the condition so that the below code outputs Hello World.

#include <stdio.h> int main() { if() { printf("Hello "); } else { printf("World\n"); } return 0; }

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#include <stdio.h>
int main()
{
    if()
    {
printf("Hello ");
    }
    else
    {
printf("World\n");
    }

    return 0;
}
Write a one line code to check if a number is a power of 2.
Write a one line code to invert the last four bits of an integer.

C Coding Questions

Questions from Datatypes

Questions from Pointers

Some codes

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