CODEWITHSUNDEEP
crecursionwhile-loopoutputtail-recursion
Drizzy
Drizzy

Reputation: 105

Recursive function to add values is outputting unusual values

I have a program that uses a tail recursion function to add the value entered and all the previous values. For example if the user enters 3, the function calculates 3+2+1 and gets an answer of 6. However this only sometimes works.

Here is my code below: 

int addNum(int n);

int main(int argc, char *argv[]) {
  int num;
  printf("Enter an integer greater than zero, (q to quit): \n");
  while(scanf("%d", &num) > 0){
      if(num < 0){
          continue;  
      }
      else if(num == 0){

          printf("Answer = 0 \n");
      }
      else{

          printf("Answer = %d \n", addNum(num)); 
      }
      printf("Enter a positive number: \n");

  }
  return 0;
}

int addNum(int n){
  int answer;
  if(n > 0){
    answer = n += addNum(n - 1);   
  }
  return answer;
}

The output I get from this code is very peculiar. For numbers 0-6 I get the right answers. Once I get to 7 and 8 both the answers are incorrect. I keep going and 9-12 the answers are correct again. Then 13 and 14 are incorrect. It keeps going back and fourth like this. I have absolutely no clue what is going on if someone could help. If it is something simple and wrong with my code please don't give me the answer but rather a hint at the problem.

I will post the output below so you can see what is going on. I decided to use pastebin for my output to save room. http://pastebin.com/DjJfxJAT

Upvotes: 1

Views: 56

Answers (2)

venkata siva Kumar
venkata siva Kumar

Reputation: 27

I think this code itself explains things

int addNum(int n);
int answer=0;
int main(int argc, char *argv[]) {


  int num;

  printf("Enter an integer greater than zero, (q to quit): \n");


  while(scanf("%d", &num) > 0){


      if(num < 0){
          continue;
      }
      else if(num == 0){

          printf("Answer = 0 \n");
      }
      else{
          answer=0;
          printf("Answer = %d \n", addNum(num));
      }

      printf("Enter a positive number: \n");

      }

  return 0;
}
  int addNum(int n){


      if(n > 0){

        answer = n += addNum(n - 1);
      }
      return answer;
  }

Upvotes: -1

Joseph Sible-Reinstate Monica
Joseph Sible-Reinstate Monica

Reputation: 48572

You don't initialize answer in addNum(), so whenever you call it with n == 0, undefined behavior occurs since you end up returning an uninitialized value. It's only by luck that you ever get the right answer.

Upvotes: 3

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