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<p><a href="https://projecteuler.net/problem=8" target="_blank">Problem 8</a> solution
<a href="#details">More...</a></p>
<div class="textblock"><code>#include &lt;stdio.h&gt;</code><br />
<code>#include &lt;stdlib.h&gt;</code><br />
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Include dependency graph for sol1.c:</div>
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Functions</h2></td></tr>
<tr class="memitem:a9ffc8845f17b01a353767a40a3adf7bd"><td class="memItemLeft" align="right" valign="top">long long int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../dc/d63/problem__8_2sol1_8c.html#a9ffc8845f17b01a353767a40a3adf7bd">get_product</a> (FILE *fp, long start_pos, int num_digits)</td></tr>
<tr class="memdesc:a9ffc8845f17b01a353767a40a3adf7bd"><td class="mdescLeft">&#160;</td><td class="mdescRight">Compute the product of two numbers in a file. <a href="../../dc/d63/problem__8_2sol1_8c.html#a9ffc8845f17b01a353767a40a3adf7bd">More...</a><br /></td></tr>
<tr class="separator:a9ffc8845f17b01a353767a40a3adf7bd"><td class="memSeparator" colspan="2">&#160;</td></tr>
<tr class="memitem:a0ddf1224851353fc92bfbff6f499fa97"><td class="memItemLeft" align="right" valign="top">int&#160;</td><td class="memItemRight" valign="bottom"><a class="el" href="../../dc/d63/problem__8_2sol1_8c.html#a0ddf1224851353fc92bfbff6f499fa97">main</a> (int argc, char *argv[])</td></tr>
<tr class="memdesc:a0ddf1224851353fc92bfbff6f499fa97"><td class="mdescLeft">&#160;</td><td class="mdescRight">Main function. <a href="../../dc/d63/problem__8_2sol1_8c.html#a0ddf1224851353fc92bfbff6f499fa97">More...</a><br /></td></tr>
<tr class="separator:a0ddf1224851353fc92bfbff6f499fa97"><td class="memSeparator" colspan="2">&#160;</td></tr>
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<a name="details" id="details"></a><h2 class="groupheader">Detailed Description</h2>
<div class="textblock"><p ><a href="https://projecteuler.net/problem=8" target="_blank">Problem 8</a> solution </p>
<dl class="section author"><dt>Author</dt><dd><a href="https://github.com/kvedala" target="_blank">Krishna Vedala</a> </dd></dl>
</div><h2 class="groupheader">Function Documentation</h2>
<a id="a9ffc8845f17b01a353767a40a3adf7bd" name="a9ffc8845f17b01a353767a40a3adf7bd"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a9ffc8845f17b01a353767a40a3adf7bd">&#9670;&#160;</a></span>get_product()</h2>
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<td class="memname">long long int get_product </td>
<td>(</td>
<td class="paramtype">FILE *&#160;</td>
<td class="paramname"><em>fp</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">long&#160;</td>
<td class="paramname"><em>start_pos</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">int&#160;</td>
<td class="paramname"><em>num_digits</em>&#160;</td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td>
</tr>
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<p>Compute the product of two numbers in a file. </p>
<dl class="params"><dt>Parameters</dt><dd>
<table class="params">
<tr><td class="paramdir">[in]</td><td class="paramname">fp</td><td>pointer to file that is already open </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">start_pos</td><td>line number of the first numer </td></tr>
<tr><td class="paramdir">[in]</td><td class="paramname">num_digits</td><td>number of digits on the line to multiply </td></tr>
</table>
</dd>
</dl>
<dl class="section return"><dt>Returns</dt><dd>expected product </dd></dl>
<div class="fragment"><div class="line"><span class="lineno"> 17</span>{</div>
<div class="line"><span class="lineno"> 18</span> <span class="keywordtype">char</span> ch = <span class="charliteral">&#39; &#39;</span>; <span class="comment">/* temporary variable to store character read from file */</span></div>
<div class="line"><span class="lineno"> 19</span> <span class="keywordtype">unsigned</span> <span class="keywordtype">char</span> num = 0; <span class="comment">/* temporary variable to store digit read */</span></div>
<div class="line"><span class="lineno"> 20</span> <span class="keywordtype">long</span> <span class="keywordtype">long</span> <span class="keywordtype">int</span> prod = 1; <span class="comment">/* product accumulator */</span></div>
<div class="line"><span class="lineno"> 21</span> <span class="keywordtype">int</span> count =</div>
<div class="line"><span class="lineno"> 22</span> 0; <span class="comment">/* we use this variable to count number of bytes of file read */</span></div>
<div class="line"><span class="lineno"> 23</span> </div>
<div class="line"><span class="lineno"> 24</span> <span class="comment">/* accumulate product for num_digits */</span></div>
<div class="line"><span class="lineno"> 25</span> <span class="keywordflow">for</span> (<span class="keywordtype">int</span> i = 0; i &lt; num_digits; i++, count++)</div>
<div class="line"><span class="lineno"> 26</span> {</div>
<div class="line"><span class="lineno"> 27</span> <span class="comment">/* get character from file */</span></div>
<div class="line"><span class="lineno"> 28</span> ch = getc(fp);</div>
<div class="line"><span class="lineno"> 29</span> </div>
<div class="line"><span class="lineno"> 30</span> <span class="comment">/* the ASCII codes of digits is between 0x30 and 0x39.</span></div>
<div class="line"><span class="lineno"> 31</span><span class="comment"> * any character not in this range implies an invalid character</span></div>
<div class="line"><span class="lineno"> 32</span><span class="comment"> */</span></div>
<div class="line"><span class="lineno"> 33</span> <span class="keywordflow">if</span> (ch &lt; 0x30 || ch &gt; 0x39)</div>
<div class="line"><span class="lineno"> 34</span> {</div>
<div class="line"><span class="lineno"> 35</span> <span class="keywordflow">if</span> (ch == EOF)</div>
<div class="line"><span class="lineno"> 36</span> <span class="keywordflow">return</span> 0;</div>
<div class="line"><span class="lineno"> 37</span> i--;</div>
<div class="line"><span class="lineno"> 38</span> <span class="keywordflow">continue</span>;</div>
<div class="line"><span class="lineno"> 39</span> }</div>
<div class="line"><span class="lineno"> 40</span> </div>
<div class="line"><span class="lineno"> 41</span> num = ch - 0x30; <span class="comment">/* convert character digit to number */</span></div>
<div class="line"><span class="lineno"> 42</span> <span class="keywordflow">if</span> (num == 0)</div>
<div class="line"><span class="lineno"> 43</span> {</div>
<div class="line"><span class="lineno"> 44</span> <span class="comment">/* If number is zero, we can skip the next &#39;num_digits&#39;</span></div>
<div class="line"><span class="lineno"> 45</span><span class="comment"> * because this &#39;0&#39; will repeat in the next &#39;num_digit&#39;</span></div>
<div class="line"><span class="lineno"> 46</span><span class="comment"> * multiplications. Hence, we also do not update the file position</span></div>
<div class="line"><span class="lineno"> 47</span><span class="comment"> */</span></div>
<div class="line"><span class="lineno"> 48</span> <span class="comment">/* NOTE: this is not needed but helps get results faster :) */</span></div>
<div class="line"><span class="lineno"> 49</span> <span class="keywordflow">return</span> 0;</div>
<div class="line"><span class="lineno"> 50</span> }</div>
<div class="line"><span class="lineno"> 51</span> </div>
<div class="line"><span class="lineno"> 52</span> prod *= num; <span class="comment">/* accumulate product */</span></div>
<div class="line"><span class="lineno"> 53</span> }</div>
<div class="line"><span class="lineno"> 54</span> </div>
<div class="line"><span class="lineno"> 55</span> <span class="comment">/* set file position to the next starting character + 1 */</span></div>
<div class="line"><span class="lineno"> 56</span> fseek(fp, -count + 1, SEEK_CUR);</div>
<div class="line"><span class="lineno"> 57</span> </div>
<div class="line"><span class="lineno"> 58</span> <span class="keywordflow">return</span> prod;</div>
<div class="line"><span class="lineno"> 59</span>}</div>
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<a id="a0ddf1224851353fc92bfbff6f499fa97" name="a0ddf1224851353fc92bfbff6f499fa97"></a>
<h2 class="memtitle"><span class="permalink"><a href="#a0ddf1224851353fc92bfbff6f499fa97">&#9670;&#160;</a></span>main()</h2>
<div class="memitem">
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<td class="memname">int main </td>
<td>(</td>
<td class="paramtype">int&#160;</td>
<td class="paramname"><em>argc</em>, </td>
</tr>
<tr>
<td class="paramkey"></td>
<td></td>
<td class="paramtype">char *&#160;</td>
<td class="paramname"><em>argv</em>[]&#160;</td>
</tr>
<tr>
<td></td>
<td>)</td>
<td></td><td></td>
</tr>
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</div><div class="memdoc">
<p>Main function. </p>
<div class="fragment"><div class="line"><span class="lineno"> 63</span>{</div>
<div class="line"><span class="lineno"> 64</span> <span class="keywordtype">int</span> position = 0;</div>
<div class="line"><span class="lineno"> 65</span> <span class="keywordtype">int</span> num_digits = 4;</div>
<div class="line"><span class="lineno"> 66</span> <span class="keywordtype">long</span> <span class="keywordtype">long</span> <span class="keywordtype">int</span> prod, max_prod = 0;</div>
<div class="line"><span class="lineno"> 67</span> </div>
<div class="line"><span class="lineno"> 68</span> <span class="comment">/* if second command-line argument is ge=iven,</span></div>
<div class="line"><span class="lineno"> 69</span><span class="comment"> * use it as the number of digits to compute</span></div>
<div class="line"><span class="lineno"> 70</span><span class="comment"> * successive product for</span></div>
<div class="line"><span class="lineno"> 71</span><span class="comment"> */</span></div>
<div class="line"><span class="lineno"> 72</span> <span class="keywordflow">if</span> (argc == 2)</div>
<div class="line"><span class="lineno"> 73</span> num_digits = atoi(argv[1]);</div>
<div class="line"><span class="lineno"> 74</span> </div>
<div class="line"><span class="lineno"> 75</span> <span class="comment">/* open file to read digits from */</span></div>
<div class="line"><span class="lineno"> 76</span> FILE *fp = fopen(<span class="stringliteral">&quot;digits.txt&quot;</span>, <span class="stringliteral">&quot;rt&quot;</span>);</div>
<div class="line"><span class="lineno"> 77</span> <span class="keywordflow">if</span> (!fp)</div>
<div class="line"><span class="lineno"> 78</span> {</div>
<div class="line"><span class="lineno"> 79</span> perror(<span class="stringliteral">&quot;Unable to open file&quot;</span>);</div>
<div class="line"><span class="lineno"> 80</span> <span class="keywordflow">return</span> -1;</div>
<div class="line"><span class="lineno"> 81</span> }</div>
<div class="line"><span class="lineno"> 82</span> </div>
<div class="line"><span class="lineno"> 83</span> <span class="comment">/* loop through all digits in the file */</span></div>
<div class="line"><span class="lineno"> 84</span> <span class="keywordflow">do</span></div>
<div class="line"><span class="lineno"> 85</span> {</div>
<div class="line"><span class="lineno"> 86</span> <span class="comment">/* get product of &#39;num_digits&#39; from current position in file */</span></div>
<div class="line"><span class="lineno"> 87</span> prod = <a class="code hl_function" href="../../dc/d63/problem__8_2sol1_8c.html#a9ffc8845f17b01a353767a40a3adf7bd">get_product</a>(fp, ftell(fp), num_digits);</div>
<div class="line"><span class="lineno"> 88</span> </div>
<div class="line"><span class="lineno"> 89</span> <span class="keywordflow">if</span> (prod &gt; max_prod)</div>
<div class="line"><span class="lineno"> 90</span> {</div>
<div class="line"><span class="lineno"> 91</span> max_prod = prod;</div>
<div class="line"><span class="lineno"> 92</span> position = ftell(fp) - 1;</div>
<div class="line"><span class="lineno"> 93</span> }</div>
<div class="line"><span class="lineno"> 94</span> } <span class="keywordflow">while</span> (!feof(fp)); <span class="comment">/* loop till end of file is reached */</span></div>
<div class="line"><span class="lineno"> 95</span> </div>
<div class="line"><span class="lineno"> 96</span> printf(<span class="stringliteral">&quot;Maximum product: %lld\t Location: %d^th position\n\t&quot;</span>, max_prod,</div>
<div class="line"><span class="lineno"> 97</span> position);</div>
<div class="line"><span class="lineno"> 98</span> fseek(fp, position,</div>
<div class="line"><span class="lineno"> 99</span> SEEK_SET); <span class="comment">/* move cursor to identified position in file */</span></div>
<div class="line"><span class="lineno"> 100</span> <span class="comment">/* loop through all digits */</span></div>
<div class="line"><span class="lineno"> 101</span> <span class="keywordflow">for</span> (; num_digits &gt; 0; num_digits--)</div>
<div class="line"><span class="lineno"> 102</span> {</div>
<div class="line"><span class="lineno"> 103</span> <span class="keywordtype">char</span> ch = getc(fp); <span class="comment">/* get character */</span></div>
<div class="line"><span class="lineno"> 104</span> <span class="comment">/* skip invalid character */</span></div>
<div class="line"><span class="lineno"> 105</span> <span class="keywordflow">if</span> (ch &lt; 0x30 || ch &gt; 0x39)</div>
<div class="line"><span class="lineno"> 106</span> <span class="keywordflow">continue</span>;</div>
<div class="line"><span class="lineno"> 107</span> <span class="keywordflow">if</span> (num_digits &gt; 1)</div>
<div class="line"><span class="lineno"> 108</span> printf(<span class="stringliteral">&quot;%c x &quot;</span>, ch);</div>
<div class="line"><span class="lineno"> 109</span> <span class="keywordflow">else</span></div>
<div class="line"><span class="lineno"> 110</span> printf(<span class="stringliteral">&quot;%c = %lld\n&quot;</span>, ch, max_prod);</div>
<div class="line"><span class="lineno"> 111</span> }</div>
<div class="line"><span class="lineno"> 112</span> </div>
<div class="line"><span class="lineno"> 113</span> fclose(fp); <span class="comment">/* close file */</span></div>
<div class="line"><span class="lineno"> 114</span> </div>
<div class="line"><span class="lineno"> 115</span> <span class="keywordflow">return</span> 0;</div>
<div class="line"><span class="lineno"> 116</span>}</div>
<div class="ttc" id="aproblem__8_2sol1_8c_html_a9ffc8845f17b01a353767a40a3adf7bd"><div class="ttname"><a href="../../dc/d63/problem__8_2sol1_8c.html#a9ffc8845f17b01a353767a40a3adf7bd">get_product</a></div><div class="ttdeci">long long int get_product(FILE *fp, long start_pos, int num_digits)</div><div class="ttdoc">Compute the product of two numbers in a file.</div><div class="ttdef"><b>Definition:</b> sol1.c:16</div></div>
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