I have a Factorial Program written down. I have the whole program completed and it runs without any problems. However, I want the output to look like this
Begin Factorial Program. . .
Provide number and the factorial will be computed: 4
4! is . . .
In f(4) and calling f(3) . . .
In f(3) and calling f(2) . . .
In f(2) and calling f(1) . . .
In f(1) and calling f(0) . . .
In f(0) and computing f(0). Returning 1
f(1) is 1 * 1 which equals 1. Returning
f(2) is 2 * 1 which equals 2. Returning 2
f(3) is 3 * 2 which equals 6. Returning 6
f(4) is 4 * 6 which equals 24. Returning 24
4! = 24
How would I get.
f(1) is 1 * 1 which equals 1. Returning
f(2) is 2 * 1 which equals 2. Returning 2
f(3) is 3 * 2 which equals 6. Returning 6
f(4) is 4 * 6 which equals 24. Returning 24
print out in my method
This is the method I have
public static int factorial(int num) {
if (num == 0) {
System.out.println("In f(" + num + ") and computing f(" + num
+ "). Returning " + 1);
return 1;
} else {
System.out.println("In f(" + num + ") and calling f(" + (num - 1)
+ ") . . .");
return num * factorial(num - 1);
}
which prints out
4! is . . .
In f(4) and calling f(3) . . .
In f(3) and calling f(2) . . .
In f(2) and calling f(1) . . .
In f(1) and calling f(0) . . .
In f(0) and computing f(0). Returning 1
4! = 24
Something like this should do the trick:
public static int factorial(int num) {
if (num == 0) {
System.out.println("In f(0) and computing f(0). Returning 1");
return 1;
}
System.out.printf("In f(%d) and calling f(%d) . . .%n", num,
num - 1); // #1
int factorial = factorial(num - 1);
int result = num * factorial;
System.out.printf(
"f(%1$d) is %1$d * %2$d which equals %3$d. Returning %3$d%n",
num, factorial, result); // #2
return result;
}
In f(4) and calling f(3) . . . In f(3) and calling f(2) . . . In f(2) and calling f(1) . . . In f(1) and calling f(0) . . . In f(0) and computing f(0). Returning 1 f(1) is 1 * 1 which equals 1. Returning 1 f(2) is 2 * 1 which equals 2. Returning 2 f(3) is 3 * 2 which equals 6. Returning 6 f(4) is 4 * 6 which equals 24. Returning 24 24
Notice how the factorial recursive call is sandwiched between the two print statements (we do this by storing it in a new variable as opposed to using its result in-line). As a result, all of the first print statements (#1) are executed before any of the second ones (#2), resulting in the desired format.
Also, in cases like this, printf makes much more sense and makes things a little easier to read/develop.