/* The factorial of a non-negative integer n, denoted by n! is the product of all positive integers less than or equal to n. For example, 5! = 5 x 4 x 3 x 2 x 1 = 120. This program calculates the number of trailing zeros in n! where n is any positive number less than 10^7. To manipulate large factorials, a solution by https://www.geeksforgeeks.org/factorial-large-number/ is used. */ #include #include using namespace std; // Maximum number of digits in output #define MAX 32000 // This function multiplies x with the number // represented by res[]. // res_size is size of res[] or number of digits in the // number represented by res[]. This function uses simple // school mathematics for multiplication. // This function may value of res_size and returns the // new value of res_size int multiply(int x, int res[], int res_size) { int carry = 0; // Initialize carry // One by one multiply n with individual digits of res[] for (int i=0; i> strInput; int num = stoi(strInput); int res[MAX]; // Initialize result res[0] = 1; int res_size = 1; // Apply simple factorial formula n! = 1 * 2 * 3 * 4...*n for (int x=2; x<=num; x++) res_size = multiply(x, res, res_size); string fStr = ""; for(int i=res_size-1; i>=0; i--) fStr += to_string(res[i]); int trailZeroes = 0; if(fStr.substr(fStr.length()-1,1) == "0"){ trailZeroes++; int pos = fStr.length()-2; while(fStr.substr(pos,1) == "0"){ trailZeroes++; pos--; } } cout << strInput << "! = " << fStr << " and it has " << trailZeroes << " trailing zeroes." << endl; return 0; }

[C++] Factorial Zeroes