Operators and Basic I/O Operatio

LT3 Basic Syntax - Operators and Basic I/Operations

Operators & Punctuators

An operator specifies an operation on values: + - * / % ++ -- >> <<

• The values are called Operands of the operator

Increment & Decrement Operators

1. Post-Increment & Post-Decrement Operators: c++ & c--

• Return the origin value, then operate

2. Pre-Increment & Pre-Decrement Operators: ++c & --c

• Operate first, then return the manipulated value

Predecence & Associativity of Operators

An expression may have multiple operators.

• Its precise meaning depends on the predecence and associativity of the operators

1. Predecence: order for different operators: + - are behind * /
2. Associativity: order for operators with same precedence:
   • an expression like x R y R z should be evaluated L-R or R-L

Operator Predecence (Hi to Lo)

1. ::
2. . -> [], LTR
3. (force to define predecence) post++ post--, LTR
4. Prefix + -, ++pre --pre, RTL
5. * / %, LTR
6. + -, LTR
7. =, +=, -=, *=, /=, RTL: Evaluate the right value, and then pass to left

An Important Notice For Postfix Increment & Decrement

Although the predecence of c++ and ++c is high,

The evaluation immediately returns the value of c

However the increment / decrement operation, will be executed after all else is done

Assignment Operator

variable = expression;

the return value is the value of the RHS expression

a = (b = 1) + (c = 2) // a = 1 + 2

Efficient Assignment Operators:

+=, -=, *=, /=, %=

Basic IO

• cin >> keyboard
• cout << screen

The Output Operator: <<

• Predefined for all standard C++ data types
• send bytes to the output device
• predfined manipulators can be used for formatting

Manipulators: #include<iomanip>

1. Weights (right-aligning)

   1. cout.width(5); // no need of <iomanip>
   2. cout<<setw(5)<<"Hi"; // output "___Hi", right alighed
      • Leading fillings are added before any value fewer than the width
      • Effective only for once, have to call every times

2. Precision: cout<<setprecesion()

   Floating-point type's precision is 6, by default

   • Permanent Effect
   • can use fixed / scientific to set the number of digits AFTER the DECIMAL POINT
   1. fixed: fixed digits after the decimal point
      `cout<<setprecision(2)<<fixed<<12.18642; // 12.19
   2. scientific: Always use the scientific notation, fix the digits after decimal (1-9).(0-9){precision}
      cout<<setprecision(2)<<scientific<<12334.123; // 1.23e+04

3. Other Manipulators

   1. setfill('x'): change the blank filling into other chars e.g.: '*'
   2. Radix: << oct / dec / hex <<
   3. Alignment: << setiosflags(ios::left) << setw(20); change the alignment of width from right to left