I. Boolean expressions
 A. Boolean values
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      BOOLEAN VALUES IN C

For purposes of conditionals
(if-statements, conditional expressions)
0
non-zero

With
#include <stdbool.h>
the type bool
and two values: 


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 B. Boolean Expressions
  1. Boolean operators
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       OPERATORS ON BOOLEANS

Negation:
      !   like
      
Short-circuit operators:

      &&  like
      ||  like

true && B == 
false && B == 

true || B ==
false || B ==


Bit-wise operators

      &
      |
      ~
      ^

07 & 07 ==
05 & 07 ==
01 & 07 ==
00 & 00 ==

07 | 00 ==
05 | 07 ==
05 | 02 ==
05 | 03 ==
03 | 00 ==

~07 == 
~06 ==
~05 ==
~04 ==

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  2. Boolean-valued expressions
------------------------------------------
     BOOLEAN-VALUED EXPRESSIONS

Comparisons have _Bool values:

 2 < 3
 3 > 2
 2 == 2
 2 != 3
 !(2 == 3)
 3 <= 3
 2 <= 3
 3 >= 2
 3 >= 3
 

Be sure to use == for comparisons
 2 = 2  // error!

 int v = 0;
 if (v = v) {           // wrong!
     printf("true\n");
 } else {
     printf("false\n");
 }

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II. Conditionals in C
 A. conditional expressions
------------------------------------------
          CONDITIONAL EXPRESSIONS

Purpose:
   to compute a value based on the program's
   state


Syntax:

  <expr> ::= <expr> ? <expr> : <expr>

Examples:

  (d != 0.0 ? n / d : 10.0)
  (n > 0 ? sqrt(n) : 0.0)

Semantics:





------------------------------------------
------------------------------------------
      &&, || ARE SYNTACTIC SUGARS

E1 && E2  ==> 

E1 || E2   ==>


So "&&", "||" are short-circuit operators,
the only evaluate their second argument
if necessary

 Examples:

     d!=0 && n/d > 3.0
     n<0 || sqrt(n) < 100.0
     
------------------------------------------
   How is this different than the Python conditional expressions?
 B. if-statements
------------------------------------------
       IF-STATEMENTS

Purpose:
   to control what actions are executed
   based on the program's state.

Syntax:

  <stmt> ::= ...
           | 


  <stmt> ::= ...
           | { <compound-stmt> }

  <compound-stmt> ::= <stmt> | <decl>
                | <stmt> <compound-stmt>
                
Examples:

    if (i < len) {
       sum = sum + i;
    }

    if (i < len) {
       sum = sum + i
    } else {
       ;
    }

    if (num == 1) {
       return "one";
    } else if (num == 2) {
       return "two";
    } else if (num == 3) {
       return "three";
    } else {
       return "more";
    }

Semantics:
    evaluates the first <expr>,



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   How is the if-statement in C different than the if-statement in Python?
------------------------------------------
            FOR YOU TO DO

Write a function int max(int x, int y)
that returns the larger of the ints x and y
passed as arguments, so that if after
    res = max(x,y)
the following holds:
    res >= x and res >= y.







------------------------------------------
 C. switch-statements
------------------------------------------
           SWITCH STATEMENTS

Purpose:



Syntax:

 <stmt> ::= ...
          | switch 
          | case
          | break;
          | default

 <const-expr> ::= <expr>  // known at compile time

   integer constant expressions can be:
      integer literals, e.g., 3, 9, 'c',
      sizeof expressions, e.g., sizeof(buf)
      a macro that is an integer constant,
          e.g., NULL, true
      ...
------------------------------------------
------------------------------------------
             SEMANTICS
             
Semantics:
      case N: and default: are



      break;



   Usual case of a switch is something like:
   
      switch (E) {
         case N1:
         case N2:
             S12
             break;
         case N3:
             S3
             break;
         default:
             S4
     }

     which is equivalent to:














------------------------------------------
------------------------------------------
           EXAMPLE

    switch (num) {
        case 1:
            res = "one";
            break;
        case 2:
            res = "two";
            break;
        case 3:
            res = "three";
            break;
        default:
            res = "more";
            break;
    }
    return res;
------------------------------------------
    How does this relate to the if-statment we wrote earlier?
  1. fall though of cases
------------------------------------------
       BEWARE: CASES MAY FALL THROUGH!

By default, code for a case may continue
into the next case(s).

What is the final value of res
when num == 1?

    switch (num) {
        case 1:
            res = "one";
        case 2:
            res = "two";
        case 3:
            res = "three";
        default:
            res = "more";
    }


Moral: Always use
   break;
at the end of each case!

Think of the syntax as:

 <stmt> ::= ... | <switch-body>
 <switch-body> ::= { <case-list> <default-stmt> }
 <case-list> ::= <case-clause>
               | <cause-clause> <case-list>
 <case-clause> ::= <case-label-list>
                     <stmt>
                     break;
 <case-label-list> ::= case <const-expr> :
                     | case <const-expr> :
                       <case-label-list>
 <default-stmt> ::= default:
                     <stmt>
                     break;
                  | default:   // at the end
                     <stmt>
------------------------------------------
  2. example
------------------------------------------
          FOR YOU TO DO

Using a switch statment,
write a function:
   int parse_answer(char c)
that returns
   0 if c is 'n' or 'N'
   1 if c is 'y' or 'Y'
   2 otherwise














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