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Topic: Get array value index by searching value (Read 3703 times) previous topic - next topic

niekwoo10

In a project i'm making, i need to use arrays. Now i have a question:
Is there a way to find a value's index just by searching for the value?

For example:

int arrayVals[] = {2, 4, -8, 3, 5, 1};

Now for example when i input "-8" into a function, i need it to return the index of -8, which is 2. How would i go about doing that?

Oh and how can i get the length of an array?

WizenedEE

To do inverse lookup you need to traverse the array
Code: [Select]

const int arysz = 6;
int ary[arysz] = {4, 32, 6, 2, -1, 5}
int wantedval = -1;
int wantedpos;
for (int i=0; i<arysz; i++) {
   if (wantedval = ary[i]) {
     wantedpos = i;
     break;
   }
}

If they're in order, you can also do a binary search (google it)

For finding array length, the best method is to use the above method and store a separate variable for the length. However, this works, too
Code: [Select]

int ary[12];
int len = sizeof(ary)/sizeof(ary[0])

niekwoo10


To do inverse lookup you need to traverse the array
-code-


Thank you. Now what happens when i search for a value that isn't in the array?

Grumpy_Mike

Then wantedval = -1 and you know you didn't find it.
Note make the initial value of wantedval outside the range of numbers you are expecting in the array.

niekwoo10

Will this code work if i expand the array during execution of the code?

AWOL

If your array is ordered, you can shorten search times by doing a binary search.
"Pete, it's a fool looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.

niekwoo10


If your array is ordered, you can shorten search times by doing a binary search.


It's not ordered.

Grumpy_Mike

Quote
Will this code work if i expand the array during execution of the code?

You can't do that, the array size is fixed by:-
Code: [Select]
int ary[arysz] = {4, 32, 6, 2, -1, 5}
You can't expand this once it has been set.

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