program To find the repetition of a number

Question

here's a problem that I can't figure it out The program should count the repetition of a number but when I run the program it seems that the function calls itself once not until the array ends as it's required any help? This is the code please have a look :)

    #include <stdio.h>
int count(int arr[],int counter,int size, int num,int i) {
    if (size != 0) {
        while (i<10) {
            if (arr[size - i] == num) {
                count(arr, size, counter++, num, i++);
            }

            else
            return counter;

        }

}

int main() {
    int result,n,i=1;
    int arr[] = {1,2,2,3,7,2,5,3,8,7};
    scanf("%d", &n);
    result=count(arr, 0,10,n,i);
    printf("%d", result);

    return 0;
}

When it calls itself recursively, it's doing 2 things wrong: (1) it's not returning anything (your compiler should have given you a warning about this), and (2) it's ignoring the value returned by the recursive call. — Tom Karzes, May 22 '20 at 02:16
@TomKarzes Yeah You're Right, So what should I do to fix this? — MR-Stark, May 22 '20 at 02:21
Side issue: rhetorical question: what happens in your function if you pass `0` as a size? — , May 22 '20 at 03:18
Why is `size` and `counter` reversed in your call? Is that on purpose? — , May 22 '20 at 03:20

score 0 · Answer 1 · answered May 22 '20 at 02:32

0

This might be help you:

#include <stdio.h>
int count(int arr[],int counter,int size, int num,int i) {
    if (size != 0) {
        for (;i<size;i++) {
            if (arr[i] == num) {
                counter++;
            }
        }
    }
    return counter;
}

int main() {
    int result,n,i=0,countt=0;
    int arr[] = {1,2,2,3,7,2,5,3,8,7};
    scanf("%d", &n);
    result=count(arr, countt,10,n,i);
    printf("%d", result);
    return 0;
}

answered May 22 '20 at 02:32

Göksel ÖZER

267
1
9

Yeah the code is working correctly but unfortunately I need it with recursion only :( . But, Thnx for helping bro 3> – MR-Stark May 22 '20 at 02:47

H.S. · Answer 2 · 2020-05-22T04:03:17.113

If you are using recursion to iterate over the input array, you should not loop over the same array in the recursive function.

Couple of problem in your code:

Function is not returning anything when this if condition results in false:

if (size != 0) {

Compiler must be giving warning on this regards.

Here, you are not ignoring the return value of count():

                count(arr, size, counter++, num, i++);

Your recursive function count() is supposed to return the frequency of num. So, you should receive the value returned by count() as it accumulate the frequency of num during recursive call.

This can be easily solved using recursion. You can do:

#include <stdio.h>

int count (int *arr, int counter, int size, int num) {
    // terminating condition
    if (size <= 0) {
        return counter;
    }

    // check the current processing number
    if (*arr == num) {
        counter++;
    }

    // recursive call to process next number
    return count (arr + 1, counter, size - 1, num);
}

int main() {
    int arr[] = {1,2,2,3,7,2,5,3,8,7};
    int result, n;

    printf ("Enter a number:\n");
    scanf ("%d", &n);

    result = count(arr, 0, sizeof (arr)/sizeof (arr[0]), n);

    printf ("Frequency of %d is %d\n", n, result);

    return 0;
}

Additional:

Do not hardcode the size of an array. You can use sizeof operator to get an array size at compile time, like this:
```
sizeof (arr)/sizeof (arr[0])
```
Make yourself aware of tail recursion, if you are not:
A function call is said to be tail recursive if there is nothing to do after the function returns except return its value. A tail recursive function can be easily transformed into an iterative one and hence compilers can also optimize the code for such functions by eliminating the recursion, that means, tail recursive calls run in constant stack space, i.e. they don't need to create new stack frames when they recursively call themselves. Check following for better idea:
How exactly does tail recursion work?

program To find the repetition of a number

2 Answers2