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copied!<p>Maybe I'm just old and grumpy, but the other answers I've seen seem to miss the point completely.</p> <p>C does not do array assignments, period. You cannot assign one array to another array by a simple assignment, unlike some other languages (PL/1, for instance; Pascal and many of its descendants too - Ada, Modula, Oberon, etc.). Nor does C really have a string type. It only has arrays of characters, and you can't copy arrays of characters (any more than you can copy arrays of any other type) without using a loop or a function call. [String literals don't really count as a string type.]</p> <p>The only time arrays are copied is when the array is embedded in a structure and you do a structure assignment.</p> <p>In my copy of K&R 2nd Edition, exercise 1-19 asks for a function <code>reverse(s)</code>; in my copy of K&R 1st Edition, it was exercise 1-17 instead of 1-19, but the same question was asked.</p> <p>Since pointers have not been covered at this stage, the solution should use indexes instead of pointers. I believe that leads to:</p> <pre><code>#include <string.h> void reverse(char s[]) { int i = 0; int j = strlen(s) - 1; while (i < j) { char c = s[i]; s[i++] = s[j]; s[j--] = c; } } #ifdef TEST #include <stdio.h> int main(void) { char buffer[256]; while (fgets(buffer, sizeof(buffer), stdin) != 0) { int len = strlen(buffer); if (len == 0) break; buffer[len-1] = '\0'; /* Zap newline */ printf("In: <<%s>>\n", buffer); reverse(buffer); printf("Out: <<%s>>\n", buffer); } return(0); } #endif /* TEST */ </code></pre> <p>Compile this with -DTEST to include the test program and without to have just the function <code>reverse()</code> defined.</p> <p>With the function signature given in the question, you avoid calling <code>strlen()</code> twice per line of input. Note the use of <code>fgets()</code> — even in test programs, it is a bad idea to use <code>gets()</code>. The downside of <code>fgets()</code> compared to <code>gets()</code> is that <code>fgets()</code> does not remove the trailing newline where <code>gets()</code> does. The upsides of <code>fgets()</code> are that you don't get array overflows and you can tell whether the program found a newline or whether it ran out of space (or data) before encountering a newline.</p>

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