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copied!<p>First you need to learn how scope works in C, and how are variables passed to functions. Local Scope > Global Scope, for example, if you have a global variable named "variable", and a function with a variable also named "variable", you'll be working on the local copy of it.</p> <p>Now, with that in mind, think of this, when you pass an argument to a function, you actually make a copy of the variable, with local scope. So in your function:</p> <p>check(4, some_global_boolean, 'a');</p> <p>When you defined the function you gave each argument a name right? so when you call a function, and you instantiate each argument into a variable(of the defined type) according to the function signature. Kinda this: argument1 = value1, argument2 = value 2,..., argumenn = valuen</p> <p>Now, lets take this to your function: boolean check(int key, boolean prev_key_high, char c) => key = 4, prev_key_high = some_global_boolean, c = 'a'</p> <p>Each of this variables has a local scope, and it has the same values as the arguments/variables/values you used in the call, but the variable is in a completely different position in memory. </p> <p>Now, there are different ways to deal with this, personally I discourage people into using global variables:</p> <p>1.Instantiate a variable in your main function (static or dynamic as you wish), and work with pointers to that specific variable:</p> <pre><code> int main(int argc, char const *argv[]) { boolean some_global_boolean = true; //or false or w/e or initialize it as you wish check(4, &some_global_boolean, 'a'); return 0; } boolean check(int key, boolean * prev_key_high, char c){ if (key == LOW) { if ( *prev_key_high){ *prev_key_high = false; Serial.println(c); return true; } } else { *prev_key_high = true; return false; } } </code></pre> <p>2.If you insist in using a global variable, use it directly, or in combination with previous comment. I encourage you into learning about pointers and working with them.</p> <pre><code>boolean check(int key, char c){ if (key == LOW) { if ( some_global_boolean){ some_global_boolean = false; Serial.println(c); return true; } } else{ some_global_boolean = true; return false; } } } </code></pre>

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