C PROGRAM TO FIND 2'S COMPLEMENT

#include<string.h>
#include<stdio.h>
int main()
{
  int n,k,c=0,g='1',i,l=0;
printf("enter size");
scanf("%d",&k);
getchar();
char s[k];
char s1[k];
printf("enter string\n");
gets(s);
n=strlen(s);
for(i=0;i<n;i++)
{
if(s[i]=='0' || s[i]=='1')
        c++;
else
l++;
}
if(c!=n)
printf("no binary digits");
else
{
for(i=0;i<n;i++)
{
if(s[i]=='0')
       s1[i]='1';
else
s1[i]='0';
}
//puts(s1);
for(i=n-1;i>=0;i--)
{
          if(s1[i]=='1'&& g=='1')
{
      s[i]='0';
}
else if(s1[i]=='0'&& g=='1')
{
s[i]='1';
g='0';
}
else
{
s[i]=s1[i];
}
}
s[n]='\0';

printf("2's complement is:");
puts(s);
}
return 0;
}
OUTPUT: