user20222: I am totally beginner in Arduino, and i want to ask some questions : 
    TCCR1B = (TCCR1B & ~(0x07<<CS10)) | (2<<CS10);

What does the previous line mean? with good explaination please . 
    TCCR1A &= ~(3<<COM1A0);

for the previous line , is there difference if i wrote '1' instead of '3' ? why ? 

user20223: On the first line, you clear some bits, then set some bits in the same “region” of the byte.
From inside out, get 7 (which is 3 bits of ones: 00000111), shift it upwards (the << operation) by CS10 amount (we don’t know how much, but the compiler does), complement all that (the tilde ~ character) and bitwise ‘and’ it with the value of the TCCR1A register (the & operation). Next, take a 2 (binary 00000010), shift it up by CS10 bits again (<< CS10), and bitwise ‘or’ that bit pattern with the earlier result (the | operator). Finally, assign all that to TCCR1A.
For the second line, yes, changing 3 to 1 will certainly change what happens to TCCR1A. It makes a different bit pattern, and I'm sure you can reason it out after reading the previous explanation.

20222: <p>I am totally beginner in Arduino, and i want to ask some questions : </p>

<pre><code>    TCCR1B = (TCCR1B &amp; ~(0x07&lt;&lt;CS10)) | (2&lt;&lt;CS10);
</code></pre>

<p>What does the previous line mean? with good explaination please . </p>

<pre><code>    TCCR1A &amp;= ~(3&lt;&lt;COM1A0);
</code></pre>

<p>for the previous line , is there difference if i wrote '1' instead of '3' ? why ? </p>
 20223: <p>On the first line, you clear some bits, then set some bits in the same “region” of the byte.</p>

<p>From inside out, get 7 (which is 3 bits of ones: 00000111), shift it upwards (the &lt;&lt; operation) by CS10 amount (we don’t know how much, but the compiler does), complement all that (the tilde ~ character) and bitwise ‘and’ it with the value of the TCCR1A register (the &amp; operation). Next, take a 2 (binary 00000010), shift it up by CS10 bits again (&lt;&lt; CS10), and bitwise ‘or’ that bit pattern with the earlier result (the | operator). Finally, assign all that to TCCR1A.</p>

<p>For the second line, yes, changing 3 to 1 will certainly change what happens to TCCR1A. It makes a different bit pattern, and I'm sure you can reason it out after reading the previous explanation.</p>
