CODEWITHSUNDEEP
c++crecursionreturnreturn-value
Brandon Smith
Brandon Smith

Reputation: 85

Return from Recursion (c/c++)

I'm having trouble returning a desired value in a recursive call. I want it to always return 0 unless a certain condition is met, in that case it should return 1 and exit.

int check = recursion(a, b, c, d, e, f);
int recursion(int *a, int *b, int c, int d, int e, int f){
    int k, dX, dY;
    for(k=0;k<=b[1]-1;k++){
        dX = b[k*4+3] - e;
        dY = b[k*4+2] - f;
        if(((dX == 1 || dX == -1) && (dY == 0))){
            if(b[k*4+4] == 1) return 1; 
            e = b[k*4+3];
            f = b[k*4+2];
            b[k*4+2] = b[k*4+3] = 0;
            recursion(a, b, c, d, e, f);
        }
        if(((dY == 1 || dY == -1) && (dX == 0))){
            if(b[k*4+4] == 1) return 1;
            e = b[k*4+3];
            f = b[k*4+2];
            b[k*4+2] = b[k*4+3] = 0;
            recursion(a, b, c, d, e, f);      
        }
    }
    return 0;   
}

A lot of irrelevant information has been removed, but as you can see if b[k*4+4] == 1 at anypoint, check should then equal 1. Otherwise, return 0 and check will = 0. It completes a basic traversal, which I know is completing correctly and is even stopping at the terminating condition (b[k*4+4] == 1) but it isn't returning the correct value.

Currently, it is ALWAYS returning 0. Check always equals 0, although it is stopping once the condition is met. I also tried removing the ending return 0; although check still equals zero...

Upvotes: 0

Views: 236

Answers (2)

Red Alert
Red Alert

Reputation: 3816

You need to do return recursion(a, b, c, d, e, f); instead of just recursion(a, b, c, d, e, f);. Otherwise, the result of those recursive calls will be lost.

edit: to not prematurely exit your loop, you can do this:

int check = recursion(a, b, c, d, e, f);
int recursion(int *a, int *b, int c, int d, int e, int f){
    int k, dX, dY;
    for(k=0;k<=b[1]-1;k++){
        dX = b[k*4+3] - e;
        dY = b[k*4+2] - f;
        if(((dX == 1 || dX == -1) && (dY == 0))){
            if(b[k*4+4] == 1) return 1; 
            e = b[k*4+3];
            f = b[k*4+2];
            b[k*4+2] = b[k*4+3] = 0;
            if(recursion(a, b, c, d, e, f) == 1)
                return 1;
        }
        if(((dY == 1 || dY == -1) && (dX == 0))){
            if(b[k*4+4] == 1) return 1;
            e = b[k*4+3];
            f = b[k*4+2];
            b[k*4+2] = b[k*4+3] = 0;
            if(recursion(a, b, c, d, e, f) == 1)
                return 1;   
        }
    }
    return 0;   
}

Upvotes: 0

creichen
creichen

Reputation: 1768

You just need to check the return values of your recursive calls, i.e.,

return recursion(a, b, c, d, e, f);

Upvotes: 1

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