字符串函數的實現

1.strlen

int strlen_mothed(const char *str)
{
assert(str != NULL);    
int count=0;
while(str[count]!='\0')
count++;
return count;
}

2.strcat

char * strcat_mothed(char *strDest,const char *strSrc)
{
  char *address=strDest;
  assert((strDest!=NULL)&&(strSrc!=NULL));
  int i=0;
  while(strDest[i]!='\0')
  {
    i++;
  }

  int j=0;
  while(strSrc[j]!='\0')
  {
    address[i++]=strSrc[j++];
  }
  address[i]='\0';
  return address;
}

3.strcmp

int strcmp_mothed(char *a,char *b)
{
  int count1=0,count2=0;

  while(a[count1]!='\0')
    count1++;
  while(b[count2]!='\0')
    count2++;

  bool change=false;
  if(count1<count2)
  {
    int t;
    t=count1;
    count1=count2;
    count2=t;
    change=true;
  }

  for(int i=0;i<count1;i++)
  {
    if(i==count2)
    {
      if(change)
      return -1;
      else
      return 1;
        
    }

    if(a[i]<b[i])
    {
      return -1;
    
    }
    else if(a[i]>b[i])
    {
      return 1;
    }

  }
  return 0;
}