knr/5.5.c

#include <stdio.h>
//#include "5.4.c"


/* char *strncpy(s,ct,n)	copy at most n characters of string ct to s; return s. Pad with '\0''s if ct has fewer than n characters. */

/* char *strcat(s,ct)	concatenate string ct to end of string s; return s. */
//char *strcat(s,ct);

/*   int strncmp(cs,ct,n)	compare at most n characters of string cs to string ct; return <0 if cs<ct, 0 if cs==ct, or >0 if cs>ct. */
//int strncmp(cs,ct,n);

char* strncpy(char* s,char* ct,int n);
char *strcat(char* s,char* ct);
int strncmp(char* cs,char* ct,int n);
void teststrncpy();
void teststrcat();
void  strncmptest();

int main()
{
  strncmptest();
  return(0);
}

void teststrcat()
{
  char p1[100];
  
  for (int i=0;i<100;i++)
    p1[i]=0;
  for (int i=65;i<91;i++)
    p1[i-65]=(char)i;
  
  char *p2;
  p2="this is also a string";
  printf("%s",strcat(p1,p2));
}

void teststrncpy()
{
  char *p1;
  p1="this is a string";
  char p2[25];
  char *ptop2 = p2;
  for (int i=0; i<25;i++)
    p2[i]=0;
  printf("%s",strncpy(p2,p1,5));
}

/* char *strncpy(s,ct,n)	copy at most n characters of string ct to s; return s. Pad with '\0''s if ct has fewer than n characters. */
char* strncpy(char* s,char* ct,int n)
{
  char* tempptr=s;
  if (ct == 0) return ct;
  for (int i =0; i<n; i++) // limit to max n chars
    {
	 if ((*ct)!=0)  
	   {
		(*tempptr)= (*ct);
          tempptr++;
          ct++;
	   }
	 else
	   {
		(*tempptr)=0; 
		return s;
	   }
    }
  return s;
}

/* char *strcat(s,ct)	concatenate string ct to end of string s; return s. */
/* no checking AT ALL on this one. good luck with yer bounds*/
char *strcat(char* s,char* ct)
{
  char* tempptr= s;    //we'll need this for returning to the calling function
  if (ct==0) return 0; //fail if there's no string to copy.
  while (*s!=0) s++;   //find spot in output string to start copying to.
  s--;                 //off by one
  do
    {
      s++;             
      *s=*ct;
      ct++;
    }
  while ( *ct!=0);
  s++;
  *s=0;                 //append trailing 0
  return tempptr;       //return string
}

void strncmptest()
{
  printf("%d \n",strncmp("12345","12345",3));
}

/*compare at most n characters of string cs to string ct; return <0 if cs<ct, 0 if cs==ct, or >0 if cs>ct. */
int strncmp(char* cs,char* ct,int n)
{
  if ((ct==0) && (ct==0)) return -6;
  if (cs==0) return -2;
  if (ct==0) return -4;
  
  for (int c=0; c<=n;c++)
    {
      if ((*cs)>(*ct)) return 1;
      else if ((*cs)<(*ct)) return -1;
      else
        {
          ct++;
          cs++;
        }
    }
  
  return 0;
}
   
   
   
/* int strncmp(char cs[],char ct[],int n)
{
  if (cs == 0) return -2;
  if (ct == 0) return -2;
  for (int i=0; i < n; i++) //limit n;
  {
    if (*cs == *ct)
	 i++;
    if (*cs > *ct) return 
      return 1;
    if (*cs < *ct) return 
      return -1;
  }
  return 0;
}
*/