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POCannot calculate factorials bigger than 20! ! How to do so?
 

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  1. POCannot calculate factorials bigger than 20! ! How to do so?
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    <p>I am using unsigned long long integer format in order to calculate big factorials. However my code fails at some point can you have a look at it? Actually it is part of a larger code for Taylor expansion of exponential function, but that part is irrelevant at this point. I will appreciate any suggestions. </p> <p>Thanks</p> <pre><code>#include &lt;stdio.h&gt; #include &lt;math.h&gt; //We need to write a factorial function beforehand, since we //have factorial in the denominators. //Remembering that factorials are defined for integers; it is //possible to define factorials of non-integer numbers using //Gamma Function but we will omit that. //We first declare the factorial function as follows: unsigned long long factorial (int); //Long long integer format only allows numbers in the order of 10^18 so //we shall use the sign bit in order to increase our range. //Now we define it, unsigned long long factorial(int n) { //Here s is the free parameter which is increased by one in each step and //pro is the initial product and by setting pro to be 0 we also cover the //case of zero factorial. int s = 1; unsigned long long pro = 1; if (n &lt; 0) printf("Factorial is not defined for a negative number \n"); else { while (n &gt;= s) { printf("%d \n", s); pro *= s; s++; printf("%llu \n", pro); } return pro; } } int main () { int x[12] = { 1, 5, 10, 15, 20, 100, -1, -5, -10, -20, -50, -100}; //Here an array named "calc" is defined to store //the values of x. unsigned long long k = factorial(25); printf("%llu \n", k); //int k; ////The upper index controls the accuracy of the Taylor Series, so ////it is suitable to make it an adjustable parameter. //int p = 500; //for ( k = 0; k &lt; p; k++); } </code></pre>
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    1. CO20! is becoming a thing now. :) Since it's right at the limit of overflowing a 64-bit integer.
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    2. CORead [Which data type or data structure to choose to calculate factorial of 100?](http://stackoverflow.com/questions/15205587/which-data-type-or-data-structure-to-choose-to-calculate-factorial-of-100/15205645#15205645)
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      1. USGrijesh Chauhan
 

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