moving from gitlab

002Factorial/factorial.c

@@ -0,0 +1,47 @@
+#include <stdio.h>  // output to terminal
+#include <stdlib.h> // has our atoi method
+
+long factorial(int n);
+
+int main(int argc, char **argv) {
+
+  // get first to arguments passed
+  // very first is name of program
+  printf("argv[0]: %s\n", argv[0]);
+  // argv[0] = ./nameofexecutable
+  // argv[1] will be our value to caluclate factorial
+
+  if (argc < 2) {
+    printf("error: value to calculate factorial is missing");
+    printf("\tUsage: ./factorial 3\n\twhere 3 is the value to calculate\n");
+    return -1;
+  }
+  // convert our char * to an int
+  int n = atoi(argv[1]);
+
+  printf("Factorial of %d is %ld\n", n, factorial(n));
+
+  return 0;
+}
+
+// use recursion first time through?
+// then maybe show a simple for loop
+long factorial(int n) {
+
+  // factorial is annotated as N!
+  // example: 5! = 5 x 4 x 3 x 2 x 1
+  // 0! = 1
+  // so properties of math yada yada..
+  // we can: 5! = 1 x 2 x 3 x 4 x 5
+  // we can use a basic loop and go all the way up to n
+  long answer = 1;
+  for (int i = 1; i <= n; i++) {
+    // answer = answer * i;
+    answer *= i;
+  }
+  return answer;
+
+  if (n == 1)
+    return 1;
+  return n * factorial(n - 1);
+}