C Coding Questions

1. Consider the following program:

   #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?

2. 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)
   
   

3. 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;
   }

4. 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;
   }

5. 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;
   }

6. 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;
   }

7. 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;
   }

8. 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;
   }

9. 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;
   }

    

10. 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;
    }

Questions from Datatypes

1. 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;
   }

2. 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;
   }

3. 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;
   }

4. What will be printed by the following code?

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

5. What will be printed by the following code?

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

6. 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;
   }

7. 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;
   }
   

Questions from Pointers

1. What will be the output of the following code?

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

2. 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 );
   }

3. What will be the output of the following code?

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

4. 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");
     }
   }

5. What will be the output of the following code?

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

6. 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);
   }

7. 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);
   }

8. 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);
   }

Some codes

1. What is the following function doing?

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

2. What is the following function doing?

   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;
   }

3. What is the following function doing?

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

4. What is the following function doing?

   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;
   }

5. What is the following function doing?

   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;
   }

6. Write the code to dynamically allocate a 2-D array of size m x n.
7. Declare a pointer to a function accepting an integer and returning void.
8. 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;
   }

9. Write a one line code to check if a number is a power of 2.
10. Write a one line code to invert the last four bits of an integer.