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Beau­tiful Racket / racket school 2019

Day 3

Mission

Imple­ment these language features:

  1. the equality compar­ison oper­a­tors == and !=

    var a = 1;
    var b = 2;
    a == b; // #false
    a != b; // #true
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    var a = 1;
var b = 2;
a == b; // #false
a != b; // #true
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  2. condi­tionals: if with optional else

    var a = 1;
    var b = 2;
    if ( a != b ) {
       alert("neq");
    }

    if ( a == b ) {
       alert("eq");
    } else {
       alert("still neq");
    }
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    var a = 1;
var b = 2;
if ( a != b ) {
   alert("neq");
}

if ( a == b ) {
   alert("eq");
} else {
   alert("still neq");
}
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    Result:

    ALERT! neq
    ALERT! still neq
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2
    ALERT! neq
ALERT! still neq
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  3. condi­tional loop: while

    var a = 0;
    while ( a != 5 ) {
        alert(a++);
    }
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    var a = 0;
while ( a != 5 ) {
    alert(a++);
}
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    Result:

    ALERT! 0
    ALERT! 1
    ALERT! 2
    ALERT! 3
    ALERT! 4
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5
    ALERT! 0
ALERT! 1
ALERT! 2
ALERT! 3
ALERT! 4
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  4. PS. if and while blocks don’t need to be termi­nated by semi­colons.

Optional

  1. Add the rela­tional oper­a­tors < <= > >=.

    var a = 0;
    var b = 1;
    a < b; // #true
    a <= b; // #true
    a > b; // #false
    a >= b; // #false
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    var a = 0;
var b = 1;
a < b;  // #true
a <= b; // #true
a > b;  // #false
a >= b; // #false
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  2. Add the rela­tional oper­a­tors && and ||.

    var a = 0;
    var b = 1;
    a < b || a > b; // #true
    a < b && a > b; // #false
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    var a = 0;
var b = 1;
a < b || a > b; // #true
a < b && a > b; // #false
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  3. Add the ternary condi­tional oper­ator.

    var a = 0;
    var b = 1;
    a < b ? "yes" : "no"; // "yes"
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    var a = 0;
var b = 1;
a < b ? "yes" : "no"; // "yes"
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    Hint: There’s prece­dence among rela­tional oper­a­tors too.

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