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Expressions - Coggle Diagram

- - - - narrowing conversion
      - widening conversion
    - - A coercion is an implicit type conversion
      - In most languages, all numeric types are coerced in
        expressions, using widening conversions
  - - - Use relational operators and operands of various types
      - Operator symbols used vary somewhat among languages
    - - Operands are Boolean and the result is Boolean
      - C has no Boolean type
  - - - Same operator is used for similar actions
      - Same operator for completely different actions
      - Same operator is used for the same action but with different data type
    - - can define nonsense
        operations
      - Readability may suffer
  - - - Change the value of variables in an expression after the execution
        of that expression
  - - - A function changes one of its parameters (two-way parameter)
      - A function changes a non-local variable
  - - - Multiple targets (PL/I)
      - Conditional targets (C, C++, and Java)
      - Compound assignment operators
      - Unary assignment operators
- - - - Negation (Unary Minus): Changes the sign of a numerical value
      - Logical NOT: Flips the truth value of a boolean expression
      - Unary + is termed as identity operator
      - Increment(++), decrement(--) operators are unary operators
    - - In C,C++, python and Java ( ? : ) is used
  - - - Define the order in which “adjacent” operators of different types are evaluated
      - Some languages (eg. APL, Smalltalk) are designed with no precedence
    - - evaluate
        
        An operator Ψ is right-associative if the expression a Ψ b Ψ c must be evaluated from right to left
        
        An operator Ψ is non-associative if expressions of the form a Ψ b Ψ c
        
        An operator Ψ is left-associative if the expression a Ψ b Ψ c must be evaluated from left to right
      - Left-to-right associativity is most common
      - Defines the order of execution of adjacent operations with the same precedence
      - Some operators are right to left associative
      - Ada the exponentiation is non associative. So, parenthesis must be used to make the statement legal
    - - determines the meaning of expressions
      - Operator evaluation order is governed by
        
        Precedence rules
        
        Associativity rules
- - - - If the next item of the expression is an operand, place it on the stack
      - If the next item of the expression is an operator that requires n operands, then replace the top n items with the result of applying this operation on the top n items
  - - - Suitable only for binary operations
      - When more than one operator appears in an expression, the notation is ambiguous unless parentheses are used
  - - - If the next item in P is an operand, push it on top of stack
      - If the top n entries in the stack are operands needed for the last operator, replace the top n + 1 entries by the result obtained by applying the last operator on the n operands above it on the stack
      - If the next item in P is an operator push it on top of the stack. Keep track of the number of operands (say n) needed by the operator