1.1.15.2 Input basic knowledge

• For Input, you need to master One basic idea, Two languages, Three data type.
• One basic idea: In order to make continuously input, you need to use while(inputMethod), When two things happens:
  1. user want to end input(ctrl+D) or read the end of File;
  2. read fail ( cin» int, but input letter ’a’),

  InputMethod will return false. Then you need use some flag or status to tell the difference between EOF or error.

• Two languages is c and c++, they use the different inputMethod. three data types are: number and word(no space in middle), character(white), and string(include space in middle)
• two languages common used input method
  

  	Number and non-white character word	Character (including white-character)	string(line)
  C	scanf("%d %f %c %s",&i, &f,&c);	int a = getchar();	fgets(stdin, char*p, n )
  C++	cin»i»f»c»w;	cin.get(char & c); Ch = cin.get();	cin.get( char *p, n); cin.getline(char *p, n); getline(cin, string);

• For C++, three get, two getline, other use »;
• Difference between cin.get(char) and int = cin.get()
  while(cin.get(c)) 
  // use cin.get(char) in reading loop 
   
  cin.get() != ’\n’ 
  //use cin.get() return character to test sth. 
   
  cin.get()!= EOF 
  //When used in EOF, you have to use int 
  //because EOF may not be expressed by char tyep
• scanf("%c" &c) and cin» c will not read white character(tab, space , newline), If you want to read them from input buffer, You should use getchar() or cin.get();
• cin » or scanf is a word-oriented reading method. Any white space, tab, new line will stop it from reading. If you want the user to input his or her name, Using cin» or scanf will terminate the string after it reads the first space. The best way to handle this situation is to use the function to read a line;
• read word and line:
  //read a word until reach white character. 
  Scanf(%s,char_array) //c 
  Cin>>char_array or ; //c++ 
  Cin>> str; 
   
  //line 
  gets(char_array)  //c 
  fgets(char_array, n , FILE *) //recommend to use this for safety. 
   
  cin.getline(char * ,int n) //c++ read and discard newline 
  cin.get(char * ,int n) //not read newline 
  std::getline(istream&  is, string& str)
• cin.read function has the same interface with cin.get, but it doesn’t append a null character to input, It’s not intend for keyboard input, but for binary format of file
• peek return the next character from input without extracting from the input stream. For example, you want to read input up to the first newline or period.
  char input[80]; 
  int i = 0; 
  while( (ch=cin.peek()) != ’.’ && ch != ’\n’) 
     cin.get(input[i++];) 
  input[i] = ’\0’;
• gcount() method returns the number of characters read by the last unfromatted extraction method. That means character read by the a get(), getline(), ignore(), or read(), but not extraction operator.
• putback() function inserts a character back in the input buffer.
• three confused functions: cin.get and cin.getline are almost the same thing.
  cin.get ( char* s, streamsize n, char delim ); 
  cin.getline (char* s, streamsize n, char delim ); 
  istream& getline (istream&  is, string& str);
  1. For each line, if you don’t know the max length, juse use getline(cin, string). You don’t need to input any length.(you can reserve lengh of string if you want to avoid allocation of memory)
  2. con.get() doesn’t discard delim from input stream. However, cin.getline() will read and discard newline. (It’s easy for you to remember, because, line is defined by newline character)
  3. In cin.getline(char* s int n)The failbit flag is set if the function extracts no characters(newline is a character), Or if the delimiting character is not found once (n-1) characters have already been written to s. Note that if the character that follows those (n-1) characters in the input sequence is precisely the delimiting character, it is also extracted and the failbit flag is not set.
  4. In cin.get(char* int n). The failbit flag is set only if the function extracts no characters.
  5. If you are talking about the newline character from a console input,it makes perfectly sense to discard it, So use cin.getline(). Or you don’t want to customized flexible reading method, just read a line from a file. please use cin.getline().
  6. cin.get(char*p, n) is more flexible than cin.getline. Because when it read to the array is full, It doesn’t set failbit. At this time you can use gcount() or peek() to see if next character is new line. It’s more customized than cin.getline();

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