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POProblem with scanf and fgets
 

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  1. POProblem with scanf and fgets
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    <p>This is for a homework assignment to sort some given strings. I'm prompting the user for the number of strings they'd like to sort with <code>scanf</code>, allocating an array based on that number, and then getting the strings themselves with <code>fgets</code>.</p> <p>Everything works fine if the number of strings is hardcoded, but the addition of <code>scanf</code> to let the user decide screws things up. Here's the code:</p> <pre><code>#include &lt;assert.h&gt; #include &lt;stdio.h&gt; #include &lt;stdlib.h&gt; #define LENGTH 20 // Maximum string length. int main(void) { int index, numStrings = 0; char **stringArray; printf("Input the number of strings that you'd like to sort: "); assert(scanf("%d", &amp;numStrings) == 1); stringArray = (char **)malloc(numStrings * sizeof(char *)); for (index = 0; index &lt; numStrings; index++) { stringArray[index] = (char *)malloc(LENGTH * sizeof(char)); assert(stringArray[index] != NULL); printf("Input string: "); assert(fgets(stringArray[index], LENGTH, stdin) != NULL); } // Sort strings, free allocated memory. return 0; } </code></pre> <p>And here's what the console looks like:</p> <pre> Input the number of strings that you'd like to sort: 3 Input string: Input string: foo Input string: bar </pre> <p>It skips over the first iteration of the loop, resulting in an empty string at the beginning of the array. My question is, why does it do that, and how can I fix it?</p> <hr> <p>Here's what the console looks with the format string <code>"%d\n"</code> passed to <code>scanf</code>:</p> <pre> Input the number of strings that you'd like to sort: 3 foo Input string: Input string: bar Input string: baz </pre> <p>So, I can input all of the strings, but the first prompt for a string is in the wrong place.</p>
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    1. CODon't `assert()` on functions that can reasonably be expected to fail, such as input functions that read user input. It is better than ignoring the error; it is not as good as handling the error sanely.
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      1. USJonathan Leffler
    2. CO@Jonathan Thanks for the advice.
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