/* This program defines and uses a function that calculates the factorial of a number Factorial has a clear pattern. In general n! is the product of the first n positive integers Example: 5! = 1*2*3*4*5 = 120. Note that 1!=1 and 0!=1 HAPPY LEARNING!!*/ /*************** CODE ************************/ #include using namespace std; int factorial(int); /* see 1*/ int main() { int number=5; /* see 2*/ cout << number << "! = " << factorial(number) << endl; /* see 3*/ return 0; } // end main() function //Below is the factorial function definition int factorial(int x) { int result=1; /* see 4*/ for(int i=2; i<=x; i++){ /* see 5*/ result *= i; } return result; /* see 6*/ } //end factorial() function /*************** COMMENTS ********************/ /* 1. The following statement is the function declaration. We cannot use a function before we declare it. We define what the function does later in the program. It is good practice to declare all functions at the beginning of the program. When we declare a function we have to specify the return type, name of the function and the argument list.*/ /* 2. Variable number is used to store the value we wish to use for the factorial. You can change the value of 'number' to test different cases. This only works for small integer values. For larger values you may use the 'long' or 'long long' data types.*/ /* 3. This statement is used to print the final results. It first displays the value of 'number' followed by the value returned by function factorial(). The 'factorial(number)' portion of this statement is a function call which prompts the execution of the statements within the function. During this function call a copy of the 'number' value will be assigned to x. When the function is done it will return an integer value which is then printed on the screen. */ /* 4. Variable 'result' is used to store the value for the factorial during execution. */ /* 5. The loop will run x-1 times. Each time it will multiply the current value of 'result' by i.*/ /* 6. When the loop is done the value of the variable 'result' is returned to the caller. */

Factorial Function - for loop - with comments