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    <p>You seem to worry a lot about type safety where there is no need for it. Since this is C and not C++, there is no strong typing system in place. Conversions from <code>unsigned char</code> to <code>char</code> are <em>usually</em> harmless, as long as the "sign bit" is never set. The key to avoiding problems is to actually understand them. The following problems/features exist in C:</p> <ul> <li>The default <code>char</code> type has implementation-defined signedness. One should never make any assumptions of its signedness, nor use it in arithmetic of any kind, particularly not bit-wise operations. <code>char</code> should only be used for storing/printing ASCII letters. It should never be mixed with hex literals or there is a potential for subtle bugs.</li> <li>The integer promotions in C implicitly promote all small integer types, among them <code>char</code> and <code>unsigned char</code>, to an integer type that can hold their result. This will in practice always be <code>int</code>.</li> <li>Formally, pointer conversions between different types could be undefined behavior. But pointer conversions between unsigned char and char are in practice safe.</li> <li>Character literals '\0' etc are of type <code>int</code> in C.</li> <li>printf and similar functions default promote all character parameters to int.</li> </ul> <p>You are also casting the void* result of malloc, which is completely pointless in C, and potentially harmful in older versions of the C standard that translated functions to "default int" if no function prototype was visible.</p> <p>And then you have various weird logic-related bugs and bad practice, which I have fixed but won't comment in detail. Use this modified code:</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; void display(const char *buff, int len) { for(int i = 0; i &lt; len; i++) { printf("buff[%d] = %c\n", i, buff[i]); } } int main() { int len = 10; unsigned char* buff = malloc(len * sizeof(unsigned char)); if(buff == NULL) { // error handling } char ch = 'A'; for(int i=0; i&lt;len; i++) { buff[i] = (unsigned char)ch + i; printf("char = %c\n", buff[i]); } printf("\nDisplaying array in main.\n"); for(int i = 0; i &lt; len; i++) { printf("buff[%d] = %u\n", i, buff[i]); } printf("\nDisplaying array in func.\n"); display((char*)buff, len); free(buff); return 0; } </code></pre>
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