Why Does `pow(10, 5)` Sometimes Return 9999 in C ?

Why pow(10,5) May Equal 9,999 in C

In C , using pow(10, 5) to calculate 10 raised to the power of 5 can occasionally result in an unexpected value of 9,999. This behavior is not consistent and can lead to confusion, as demonstrated in the following code snippet:

const int sections = 10;

for (int t = 0; t <p>The expected output of this code is [10000, 1000, 100, 10, 1], but it actually produces [9999, 1000, 99, 10, 1].</p><h3 id="Explanation">Explanation</h3><p>The cause of this issue lies in the floating-point representation of pow(10.0, 5) in C  . When the result of this calculation is stored in a double-precision floating-point variable, it may contain fractional parts. When it is then assigned to an integer variable, the fractional part is truncated, resulting in a value that is slightly less than the actual answer. In this case, pow(10.0, 5) may be represented internally as 9999.9999999, which gets truncated to 9999 when assigned to an integer.</p><h3 id="Solution">Solution</h3><p>To avoid this problem, one can use the following alternatives:</p>

• Specify the result of pow as a double-precision floating-point value: double i = pow(sections, 5 - t - 1);.
• Round the result of pow to the nearest integer using the round function: int i = round(pow(sections, 5 - t - 1));.
• Use a more precise floating-point representation, such as long double or quad double.

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