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    <p>Your function could look like this:</p> <pre><code>char* sum_str(char* s1, char* s2) { int lenS1 = strlen(s1); int lenS2 = strlen(s2); char* newString = malloc((lenS1 + lenS2 + 1) * sizeof(char)); int i = 0; while(i &lt; lenS1) { newString[i] = s1[i]; i++; } while(i &lt; lenS2 + lenS1) { newString[i] = s2[i - lenS1]; i++; } newString[i] = '\0'; return newString; } </code></pre> <p>Note that this function allocates new string which means you should <code>free</code> this data when you finish with this string. Also note that terminating character (<code>'\0'</code>) is stored at the end of this char array so that <code>printf</code> can "print" it properly.</p> <p>Here's main:</p> <pre><code>int main() { char *s1, *s2, *s3; s1 = "Joe"; s2 = " Black"; s3 = sum_str(s1,s2); printf("%s\n", s3); free(s3); return 0; } </code></pre> <p>Output: <code>Joe Black</code></p> <p>Note that I have declared variables <code>s1</code>, <code>s2</code> and <code>s3</code> like this: <code>char *s1, *s2, *s3;</code>. If I write it like this: <code>char *s1, s2, s3;</code> then variables <code>s2</code> and <code>s3</code> are no longer arrays of characters but only characters.</p> <p>Also note that this program:</p> <pre><code> char *s1 = "Joe"; s1[0] = 'X'; printf("%s\n", s1); </code></pre> <p>will crash since it tries to change constant string literal <code>"Joe"</code>. <code>s1</code> is pointer to first character of this literal in this case.</p> <p>But this program will work fine and its output will be <code>Xoe</code>:</p> <pre><code> char s1[] = "Joe"; s1[0] = 'X'; printf("%s\n", s1); </code></pre> <p><code>s1</code> is an array initialized with string <code>"Joe"</code> so it's OK to change it.</p>
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    1. POString Concatenation function in C doesn;t do anything, so what is the correct way?
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    1. COThat whole "Don't forget to free it" part is why `strcat` makes you pass in the dest buffer (and why `strncat` is better) ;)
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    2. COHe is learning basics in C, that's why I wrote this function to copy character by character so that it helps to understand how strings work in C.
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