Strange output

[junw2000@gmail.com]

I wrote a simple binary search function:

int binary_serach_R (int a[], int k, int l, int r){
int m = (l+r)/2;
if(a[m] == k){
std::cout<<"ret urn a[m] "<<a[m]<<'\n'; //LINE1
return a[m]; //LINE2
}
if(l == r) return -1;
// std::cout<<a[m]<<" "<<l<<" "<< m<<" "<<r<<'\n';
if(a[m] k) binary_serach_R (a, k, l, m);
else binary_serach_R (a, k, m, r);
}

LINE1 can always output a correct value. But LINE2 always returns a
random value,
like -1207956288. What is the problem?

Thanks.

Jack

[mlimber]

Re: Strange output


junw2000@gmail. com wrote:

I wrote a simple binary search function:
>
int binary_serach_R (int a[], int k, int l, int r){
int m = (l+r)/2;
if(a[m] == k){
std::cout<<"ret urn a[m] "<<a[m]<<'\n'; //LINE1
return a[m]; //LINE2
}
if(l == r) return -1;
// std::cout<<a[m]<<" "<<l<<" "<< m<<" "<<r<<'\n';
if(a[m] k) binary_serach_R (a, k, l, m);
else binary_serach_R (a, k, m, r);
}
>
LINE1 can always output a correct value. But LINE2 always returns a
random value,
like -1207956288. What is the problem?

You forgot to return the value from your recursive calls.

Cheers! --M

[junw2000@gmail.com]

Re: Strange output


mlimber wrote:

junw2000@gmail. com wrote:

I wrote a simple binary search function:

int binary_serach_R (int a[], int k, int l, int r){
int m = (l+r)/2;
if(a[m] == k){
std::cout<<"ret urn a[m] "<<a[m]<<'\n'; //LINE1
return a[m]; //LINE2
}
if(l == r) return -1;
// std::cout<<a[m]<<" "<<l<<" "<< m<<" "<<r<<'\n';
if(a[m] k) binary_serach_R (a, k, l, m);
else binary_serach_R (a, k, m, r);
}

LINE1 can always output a correct value. But LINE2 always returns a
random value,
like -1207956288. What is the problem?

You forgot to return the value from your recursive calls.
>

Thanks. I got it. Then where is the random value from?
Jack

[mlimber]

Re: Strange output


junw2000@gmail. com wrote:

mlimber wrote:

junw2000@gmail. com wrote:

I wrote a simple binary search function:
>
int binary_serach_R (int a[], int k, int l, int r){
int m = (l+r)/2;
if(a[m] == k){
std::cout<<"ret urn a[m] "<<a[m]<<'\n'; //LINE1
return a[m]; //LINE2
}
if(l == r) return -1;
// std::cout<<a[m]<<" "<<l<<" "<< m<<" "<<r<<'\n';
if(a[m] k) binary_serach_R (a, k, l, m);
else binary_serach_R (a, k, m, r);
}
>
LINE1 can always output a correct value. But LINE2 always returns a
random value,
like -1207956288. What is the problem?

>

You forgot to return the value from your recursive calls.

Thanks. I got it. Then where is the random value from?
Jack

It's whatever junk is in the location where your return value would get
stored (probably a value on the stack). I'm surprised your compiler let
you get away with that without warning you (or did you ignore the
warning?); if it didn't bark, you need to turn up your warning level.

Cheers! --M