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  1. PO
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    <p>While I waited for you to post this as a question I coded something up.</p> <p>This code iterates through a string passed to a "longest" function, and when it finds the first of a sequence of letters it sets a pointer to it and starts counting the length of it. If it is the longest sequence of letters yet seen, it sets another pointer (the '<code>maxStringStart</code>' pointer) to the beginning of that sequence until it finds a longer one.</p> <p>At the end, it allocates enough room for the new string and returns a pointer to it.</p> <pre><code>#include&lt;stdio.h&gt; #include&lt;stdlib.h&gt; #include&lt;string.h&gt; int isLetter(char c){ return ( (c &gt;= 'a' &amp;&amp; c &lt;= 'z') || (c &gt;= 'A' &amp;&amp; c &lt;= 'Z') ); } char *longest(char *s) { char *newString = 0; int maxLength = 0; char *maxStringStart = 0; int curLength = 0; char *curStringStart = 0; do { //reset the current string length and skip this //iteration if it's not a letter if( ! isLetter(*s)) { curLength = 0; continue; } //increase the current sequence length. If the length before //incrementing is zero, then it's the first letter of the sequence: //set the pointer to the beginning of the sequence of letters if(curLength++ == 0) curStringStart = s; //if this is the longest sequence so far, set the //maxStringStart pointer to the beginning of it //and start increasing the max length. if(curLength &gt; maxLength) { maxStringStart = curStringStart; maxLength++; } } while(*s++); //return null pointer if there were no letters in the string, //or if we can't allocate any memory. if(maxLength == 0) return NULL; if( ! (newString = malloc(maxLength + 1)) ) return NULL; //copy the longest string into our newly allocated block of //memory (see my update for the strlen() only requirement) //and null-terminate the string by putting 0 at the end of it. memcpy(newString, maxStringStart, maxLength); newString[maxLength + 1] = 0; return newString; } int main(int argc, char *argv[]) { int i; for(i = 1; i &lt; argc; i++) { printf("longest all-letter string in argument %d:\n", i); printf(" argument: \"%s\"\n", argv[i]); printf(" longest: \"%s\"\n\n", longest(argv[i])); } return 0; } </code></pre> <p>This is my solution in simple C, without any data structures.</p> <p>I can run it in my terminal like this:</p> <pre><code>~/c/t $ ./longest "hello there, My name is Carson Myers." "abc123defg4567hijklmnop890" longest all-letter string in argument 1: argument: "hello there, My name is Carson Myers." longest: "Carson" longest all-letter string in argument 2: argument: "abc123defg4567hijklmnop890" longest: "hijklmnop" ~/c/t $ </code></pre> <p>the criteria for what constitutes a letter could be changed in the <code>isLetter()</code> function easily. For example:</p> <pre><code>return ( (c &gt;= 'a' &amp;&amp; c &lt;= 'z') || (c &gt;= 'A' &amp;&amp; c &lt;= 'Z') || (c == '.') || (c == ' ') || (c == ',') ); </code></pre> <p>would count periods, commas and spaces as 'letters' also.</p> <hr> <p>as per your update:</p> <p>replace <code>memcpy(newString, maxStringStart, maxLength);</code> with:</p> <pre><code>int i; for(i = 0; i &lt; maxLength; i++) newString[i] = maxStringStart[i]; </code></pre> <p>however, this problem would be much more easily solved with the use of the C standard library:</p> <pre><code>char *longest(char *s) { int longest = 0; int curLength = 0; char *curString = 0; char *longestString = 0; char *tokens = " ,.!?'\"()@$%\r\n;:+-*/\\"; curString = strtok(s, tokens); do { curLength = strlen(curString); if( curLength &gt; longest ) { longest = curLength; longestString = curString; } } while( curString = strtok(NULL, tokens) ); char *newString = 0; if( longest == 0 ) return NULL; if( ! (newString = malloc(longest + 1)) ) return NULL; strcpy(newString, longestString); return newString; } </code></pre>
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    1. POC - Largest String From a Big One
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    1. USCarson Myers
    1. USCarson Myers
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    1. COWhat's wrong with `#include <ctype.h>` and `isalpha()`?
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      1. USJonathan Leffler
    2. COnothing I suppose, I just didn't think of it -- just that now he says he can only use `strlen`. In his last question he used `malloc` so I guess that one's still okay too.
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      1. USCarson Myers
    3. COI think that's a silly requirement - especially because your replacement function isn't guaranteed to work by the C standard (unfortunately, alphabetical characters aren't required to be consecutive, only digit characters). I think you should make a second version that uses all the standard functions, if only to show later readers how much easier this is with the standard library.
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      1. USChris Lutz
 

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