Array as arguments in function

Question

I am writing a C program to calculate Moving Average (MA) of share price. data is available in an array datavalue[count], count= is number of data values. Now i am trying to write up a function for MA.. but i have to pass three arguments in the function as follows

int count = number of data values
int K = period of moving average
array float type datavalue = array containing share pricing.

I have written following code (as part of full code for calculation MA). it is working fine.

float data[count], mag[count];
double avg, sum;

for (i=0; i<=count; i++)
   data[i] = numberArray[i];

for (i=0; i<k-1; i++) {
     mag[i-1] = 0;
     sum = sum + data[i];
}

for (i=k-1; i<=count; i++) {
    mag[i-1] = avg;
    sum = sum + data[i] - data[i-k];
    avg = sum / k;
}

Above code is working fine within single main file. but as i have to reuse MA again and again in my program, thus i decided to make a separate function for MA. i did it as follows

float *mavg(int count, int k, float datavalue)
{
    float *mag = malloc(sizeof(float)*count);
    //float data[count];
    float avg=0, sum=0;
    int i;

    for (i=0; i<=count; i++) {
        for (i=0; i<k-1; i++) {
            mag[i-1] = 0;
            sum = sum + datavalue[i];
        }
    }

    for (i=k-1; i<=count; i++) {
        mag[i-1] = avg;
        sum = sum + datavalue[i] - datavalue[i-k];
        avg = sum/k;
    }
    return mag;
}

BUT above code is not working when calling from main file. While compiling it is showing error

subscripted value is neither array nor pointer nor vector

in following lines :

sum = sum + datavalue[i];
sum = sum + datavalue[i] - datavalue[i-k];

Please explain what “not working” means. Compilation errors? Runtime errors? Wrong results? Which results, what did you expect to get? — Sami Kuhmonen
– Sami Kuhmonen, Commented Dec 16, 2018 at 8:57
while compiling it is showing error: subscripted value is neither array nor pointer nor vector ... in sum=sum+datavalue[i]; as well as in sum=sum+datavalue[i]-datavalue[i-k]; — Mohd Naved
– Mohd Naved, Commented Dec 16, 2018 at 9:01
datavalue is declared as a single float. You can’t use it as an array. You probably wanted to declare it as a pointer — Sami Kuhmonen
– Sami Kuhmonen, Commented Dec 16, 2018 at 9:02
Well it isn't, what is unclear? float datavalue) datavalue[i] — Yunnosch
– Yunnosch, Commented Dec 16, 2018 at 9:02

4386427 · Accepted Answer · 2018-12-16 09:25:44Z

2

The variable datavalue is not an array. It's defined here as a single float:

float *mavg(int count, int k, float datavalue)
                              ^^^^^
                              That is not an array

Therefore you get compiler error when doing datavalue[i]

Did you mean to do

float *mavg(int count, int k, float* datavalue)
                                  ^

Also this part seems strange:

for(i=0;i<=count;i++)     // Here you use variable i for the loop
    for(i=0;i<k-1;i++)    // and again here you use variable i for the loop
                          // Sure that is what you want?
    {
        mag[i-1]=0;       // When variable i is zero, you index with -1 which is wrong
                          // as you write outside the allocated memory

        sum=sum+datavalue[i];
    }

edited Dec 16, 2018 at 9:25

answered Dec 16, 2018 at 9:00

4386427

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1 Comment

David C. Rankin Over a year ago

Poor 'i', the little guy never had a chance... (and if k is less than count, things could go on for a very long time.)

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