Why this function return is not returning expected results in Java?

debugcn Published at Dev

jiya singh

Below is a function which takes int and return int. Within the function I call the function itself and if i==1, I want to go out of my function.

Basically I'm trying to calculate factorial in recursive manner.

Code Snippet

static int factorial(int i){
   result = result * i;
   if(i==1){
       return 0;
   }
   factorial(i-1);
   return 1;
}

Note - result is an global int variable and is initialize to 1.

Why this function returns 1 instead of 0. [Note when i==1 then with return statement the pointer should come out of the function]

Please don't post better algorithm for factorial, I'm looking for - why this code is behaving a bit different.

user14971157

example calling factorial(3):

int i = factorial(3);
    +--------------------------------------------------+
    |result = result * 3;                              |
    |if (i==1) {                                       |
    |  // not executed                                 |
    |}                                                 |
    |factorial(2);                                     |
    |    +-------------------------------------------+ |
    |    |result = result * 2;                       | |
    |    |if (i==1) {                                | |
    |    |  // not executed                          | |
    |    |}                                          | |
    |    |factorial(1);                              | |
    |    |    +---------------------------------+    | |
    |    |    |result = result * 1;             |    | |
    |    |    |if (i==1) {                      |    | |
    |    |    |  return 0;                      |    | |
    |    |    |// nothing more in factorial(1)  |    | |
    |    |    +---------------------------------+    | |
    |    |// factorial(1) returned 0 (value not used)| |
    |    |return 1;  // factorial(2)                 | |
    |    +-------------------------------------------+ |
    |// factorial(2) returned 1 (value not used)       |
    |return 1;  // factorial(3)                        |
    +--------------------------------------------------+
i = 1; // the value returned by last call

factorial(3) returns 1! _{recursion was terminated by return 0, but that value is not being used}

Zero would have been returned if the last two lines were joined to return factorial(i-1);

_{only factorial(1) will return 0, e.g. int i = factorial(1)}

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