C Program To convert the given binary number to 2’s complement

To convert the given binary number to 2’s complement

#include <stdio.h>

#include<conio.h>

void complement (char *a);

void main()

{

 char a[16];

 int i;

            clrscr();

 printf("Enter the binary number");

 gets(a);

 for(i=0;a[i]!='\0'; i++)

 {

  if (a[i]!='0' && a[i]!='1')

  {

printf("The number entered is not a binary number. Enter the correct number");

   exit(0);

                            }     

            }

complement(a);

getch();           

}

void complement (char *a)

{

            int l, i, c=0;

            char b[16];

 l=strlen(a);

 for (i=l-1; i>=0; i--)

 {

  if (a[i]=='0')

  b[i]='1';                     

 else    

 b[i]='0';

 }

 for(i=l-1; i>=0; i--)

 {

 if(i==l-1)

 {

  if (b[i]=='0')

                                      b[i]='1';

                                     else

  {

   b[i]='0';                    

c=1;

  }

 }

 else

            {

                        if(c==1 && b[i]=='0')

                         {

                                    b[i]='1';                       

 c=0;

  }

 else if (c==1 && b[i]=='1')

 {

                                    b[i]='0';                       

 c=1;

 }

}

}

b[l]='\0';

printf("The 2's complement is %s", b);

}