Decimal to binary conversion

C program to convert decimal to binary: c language code to convert an integer from decimal number system(base-10) to binary number system(base-2). Size of integer is assumed to be 32 bits. We use bitwise operators to perform the desired task. We right shift the original number by 31, 30, 29, ..., 1, 0 bits using a loop and bitwise AND the number obtained with 1(one), if the result is 1 then that bit is 1 otherwise it is 0(zero).

C programming code

#include <stdio.h>
 
int main()
{
  int n, c, k;
 
  printf("Enter an integer in decimal number system\n");
  scanf("%d", &n);
 
  printf("%d in binary number system is:\n", n);
 
  for (c = 31; c >= 0; c--)
  {
    k = n >> c;
 
    if (k & 1)
      printf("1");
    else
      printf("0");
  }
 
  printf("\n");
 
  return 0;
}

Download Decimal binary program.
Output of program:

Above code only prints binary of integer, but we may wish to perform operations on binary so in the code below we are storing the binary in a string. We create a function which returns a pointer to string which is the binary of the number passed as argument to the function.

C code to store decimal to binary conversion in a string

#include <stdio.h>
#include <stdlib.h>
 
char *decimal_to_binary(int);
 
main()
{
   int n, c, k;
   char *pointer;
 
   printf("Enter an integer in decimal number system\n");
   scanf("%d",&n);
 
   pointer = decimal_to_binary(n);
   printf("Binary string of %d is: %s\n", n, t);
 
   free(pointer);
 
   return 0;
}
 
char *decimal_to_binary(int n)
{
   int c, d, count;
   char *pointer;
 
   count = 0;
   pointer = (char*)malloc(32+1);
 
   if ( pointer == NULL )
      exit(EXIT_FAILURE);
 
   for ( c = 31 ; c >= 0 ; c-- )
   {
      d = n >> c;
 
      if ( d & 1 )
         *(pointer+count) = 1 + '0';
      else
         *(pointer+count) = 0 + '0';
 
      count++;
   }
   *(pointer+count) = '\0';
 
   return  pointer;
}

Memory is allocated dynamically because we can't return a pointer to a local variable (character array in this case). If we return a pointer to local variable then program may crash or we get incorrect result.