1.1.13.2 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 (for example, 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 inside of while loop.

• 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);

• In scanf, You need to specify exact data type when you read.
  1. h: short int or short unsigned. Example: %hd or %hu.
  2. l: a long int or long unsigned, or double (for %f conversions.) Example: %ld, %lu, or %lf.
  3. L: The value to be parsed is a long long for integer types or long double for float types. Example: %Ld, %Lu, or %Lf.
  4. *: Tells scanf() do to the conversion specified, but not store it anywhere. This is what you use if you want scanf() to eat some data but you don’t want to store it anywhere; you don’t give scanf() an argument for this conversion. Example: %*d.
• scanf("%c" &c) will read any character, including whitespace character. If you want to scanf skip any whitespace, you can use space before %c.
  while(true){ 
    scanf("%c",&c); 
    //scanf("___ %c",&c); 
    printf("you␣input:␣%d" c); 
  } 
  // When you input a(enter) 
  //output will be like 
  you input: 97(a value) 
  you input: 10(enter value)
• 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(); If you want the user to input his or her name
  while(true){ 
    cin>>c; 
    cout<<"you␣input:"<<c<<endl; 
  } 
  // When you input  "    a(enter)" 
  //output will be like 
  you input:  a 
  then cursor wait for here.
• 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
• 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
• 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. cin.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* s , 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* s, 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();