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    <p>Casts are irrelevant, it's the (possibly implicit) prototype that matters.</p> <pre><code>void foo(short s) { // do something } int main(void) { signed char c = 'a'; foo(c); // c is promoted to short by explicit prototype bar(c); // c is promoted to int by implicit prototype } void bar(int i) { // do something } </code></pre> <p>When the book says "an argument of a function call is an expression" it means that the same type promotion rules apply. It might be easier to understand if you think of a function argument as an implicit assignment to the variable specified in the function prototype. e.g. in the call to <code>foo()</code> above there's an implicit <code>short s = c</code>.</p> <p>This is why casts don't matter. Consider the following code snippet:</p> <pre><code>signed char c = 'a'; int i = (short) c; </code></pre> <p>Here the value of c is promoted first to <code>short</code> (explicitly) then to <code>int</code> (implicitly). The value of <code>i</code> will always be an <code>int</code>.</p> <p>As for <code>char</code> and <code>short</code> becoming <code>int</code> and <code>float</code> becoming <code>double</code> that refers to the default types for implicit function prototypes. When the compiler sees a call to a function before it has seen either a prototype or the definition of the function it generates a prototype automatically. It defaults to <code>int</code> for integer values and <code>double</code> for floating-point values.</p> <p>If the eventual function declaration doesn't match to implicit prototype, you'll get warnings.</p>
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    1. USMichael Carman
    1. USMichael Carman
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    1. COyour post answers many questions that I had prior to posting this question.
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      1. USMidnight Blue
    2. COGlad to help, Midnight Blue.
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      1. USMichael Carman
    3. COThis answer mixes "prototype" with "declaration". A prototype is what declares the type of function parameters. A declaration is what may include a prototype and what the whole thing is called ("void f();"). So you want to say "implicit declaration" and "explicit declaration" instead.
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      1. USJohannes Schaub - litb
 

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