MHB Completing DoublePennies(): Solving the Infinite Loop

[ksepe]

Write code to complete DoublePennies()'s base case. Sample output for below program:
Number of pennies after 10 days: 1024

The if statement is what I am trying to complete, however this places it in an infinite loop

#include <stdio.h>

// Returns number of pennies if pennies are doubled numDays times
long long DoublePennies(long long numPennies, int numDays){
   long long totalPennies = 0;

   /* Your solution goes here  */
   
[B]if (numDays==1)[/B] {
   totalPennies=DoublePennies((numPennies*2), numDays);
}
   else {
     totalPennies = DoublePennies((numPennies * 2), numDays - 1);
     }

   return totalPennies;
}

// Program computes pennies if you have 1 penny today,
// 2 pennies after one day, 4 after two days, and so on
int main(void) {
   long long startingPennies = 0;
   int userDays = 0;

   startingPennies = 1;
   userDays = 10;
   printf("Number of pennies after %d days: %lld\n", userDays, DoublePennies(startingPennies, userDays));

   return 0;
}

 

[Greg]

Why use recursion when a simple for loop will do?

 

[ksepe]

Why use recursion when a simple for loop will do?

The code was provided.. I just have to complete the base case which is what I cannot figure out...

 

[Greg]

I should have guessed. Anyway, the reason you're getting an infinite loop is that you are calling DoublePennies with numDays = 1 and numDays is not being changed. See?

Recursion can be tricky (that's why I asked about the for loop) but it's handy (as you may well know). Here's the code I'd use and I'll leave you to make another attempt in your other post and to post your work if you get stuck.

long long DoublePennies(long long numPennies, int numDays){

		static long long totalPennies;

		if (numDays == 1)
			return numPennies * 2;
		else {
			totalPennies = numPennies * 2;
			DoublePennies(totalPennies, numDays - 1);
		}
   	
	}

Note the static declaration for totalPennies.

If there's problems with that please post back here.

 

[Greg]

Actually, the static declaration isn't necessary. Sorry about that.

long long DoublePennies(long long numPennies, int numDays){

		long long totalPennies = 0;

		if (numDays == 1)
			return numPennies * 2;
		else {
			totalPennies = numPennies * 2;
			DoublePennies(totalPennies, numDays - 1);
		}
   	
}

This is correct and is in keeping with what was given by the assignment, though it's not necessary to initialize totalPennies. In fact, you could eliminate totalPennies altogether:

long long DoublePennies(long long numPennies, int numDays) {

		if (numDays == 1)
			return numPennies * 2;
		else 
			DoublePennies(numPennies * 2, numDays - 1);
}