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copied!<h3>Analysis</h3> <p>There is a wealth of problems in these few lines:</p> <pre><code>pFile = fopen("argv[1]", "r"); fscanf(pFile, "%lf", &N); while(!feof(pFile)) { fscanf(pFile, "%d", &num); </code></pre> <ol> <li>You probably wanted to open the file designated by <code>argv[1]</code>, not a file called <code>argv[1]</code>. Remove the quotes.</li> <li>You didn't check that you were passed an argument.</li> <li>You don't check that <code>fopen()</code> succeeded, so you probably crashed in your first <code>fscanf()</code>.</li> <li>You don't check that <code>fscanf()</code> succeeded. It is also odd to read what should probably be an integer value into a <code>double</code>, but the notation used will work.</li> <li>You should not use <code>feof()</code> like that, especially if …</li> <li>You don't check that the second <code>fscanf()</code> succeeded, and it won't work properly (but might not report the problem) because …</li> <li>You are trying to read integers (<code>%d</code>) into a <code>double</code>.</li> </ol> <p>So, you should have written:</p> <pre><code>if (argc <= 1) …report error and exit…(or use pFile = stdin)… FILE *pFile = fopen(argv[1], "r"); if (pFile == 0) …report error and exit… if (fscanf(pFile, "%lf", &N) == 1) { for (int i = 0; i < N; i++) { if (fscanf(pFile, "%lF", &num) != 1) …report error, close file, and exit… …as before…more or less…subject to fixing any as yet undiagnosed errors… } } fclose(pFile); </code></pre> <p>Incidentally, you forgot to set <code>sum_sqs</code> to zero before you started adding to it, so you won't know what value you got. Also, if all the numbers are negative, you'll report that the maximum is 0; if all the numbers are positive, you'll report that the minimum is 0. Fixing that is a tad fiddly, but you could use <code>if (i == 0 || num < min) min = num;</code> etc.</p> <hr> <h3>Linking Problem</h3> <p>Your linking problem (undefined reference to <code>sqrt()</code>) indicates that you are running on a system where you need to link the maths library; that is usually <code>-lm</code> on the end of the linking command line.</p> <hr> <h3>Synthesis</h3> <pre><code>#include <stdio.h> #include <math.h> int main(int argc, char*argv[]) { double average, num = 0, min = 0, max = 0, sum = 0, N, std_dev, sum_sqs = 0.0; if (argc <= 1) { fprintf(stderr, "Usage: %s file\n", argv[0]); return 1; } FILE *pFile = fopen(argv[1], "r"); if (pFile == 0) { fprintf(stderr, "%s: failed to open file %s\n", argv[0], argv[1]); return 1; } if (fscanf(pFile, "%lf", &N) == 1) { for (int i = 0; i < N; i++) { if (fscanf(pFile, "%lF", &num) != 1) { fprintf(stderr, "%s: failed to read number\n", argv[0]); return 1; } if (num < min || i == 0) min = num; if (num > max || i == 0) max = num; sum += num; sum_sqs += (num*num); } } fclose(pFile); average = sum/N; std_dev = sqrt((sum_sqs/N)-(average*average)); printf("Smallest: %7.2lf\n", min); printf("Largest: %7.2lf\n", max); printf("Average: %7.2lf\n", average); printf("Standard deviation: %7.3lf\n", std_dev); return(0); } </code></pre> <h3>Results</h3> <p>Given data file <code>data</code>:</p> <pre><code>5 4.34 23.4 18.92 -78.3 17.9 </code></pre> <p>The result of running the program is:</p> <pre><code>Smallest: -78.30 Largest: 23.40 Average: -2.75 Standard deviation: 38.309 </code></pre> <p>Those values mostly look plausible; my calculation of the standard deviation came to 42.83 (using a different tool altogether). The difference is between the sample standard deviation and the population standard deviation (a factor of √1.25) — so your value is OK as you calculated it.</p> <pre><code># Count = 5 # Sum(x1) = -1.374000e+01 # Sum(x2) = 7.375662e+03 # Mean = -2.748000e+00 # Std Dev = 4.283078e+01 # Variance = 1.834476e+03 # Min = -7.830000e+01 # Max = 2.340000e+01 </code></pre> <p>So, the code works for me. What result are you getting?</p>

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