Arduino custom-made function is not working - arduino

Question

I wrote my own Arduino function in order to measure the heart rate. But when it executes it does not work properly. In order to calculate heart rate, I have to do the following calculation:
heart_Rate = 60000/period;
But I realized that the period value keeps accumulating. As a result of that the heart rate reduces. But when I test this without making function (inside void loop) it's working perfectly.
This is my Arduino code:
int H_val = 0;
void setup() {
Serial.begin(9600);
}
float HeartRate() {
int threshold = 750;
int raw_ecg = 0;
int E_input = 0;
float period = 0;
unsigned long p_time = 0;
unsigned long c_time = 0;
int H_rate;
int oldvalue = 0;
oldvalue = raw_ecg;
raw_ecg = 0;
raw_ecg = analogRead(A0);
if (oldvalue < threshold && raw_ecg >= threshold) {
p_time = c_time;
c_time = millis();
period = c_time - p_time;
}
if (period <= 0) {
int H_rate = 0;
} else {
int H_rate = 60000 / period;
return H_rate;
}
delay(2);
}
void loop() {
H_val = HeartRate();
Serial.println(H_val);
}
How do I prevent the period from accumulating?

Answer 1

Every time you call the function, the local variables get initialized again. In your code this means that
p_time = c_time; //c_time = 0
c_time = millis();
period = c_time - p_time;
Hence, period will increase as millis() is increasing.
If you declare the variables as static, your problem will be solved:
static unsigned long p_time = 0;
static unsigned long c_time = 0;
By doing that, the variables keep existing (and keep their value) between function calls and keep their local scope.
The reason it is working inside the loop is that you never leave the loop and the variables never get re-initialized.
Edit: it's enough to declare c_time as static as you assign it's value to p_time anyway. But there are various ways to shorten the code.

Answer 2

It can be a problem of data type. Changing that variables to float or int may solve the problem.
float H_val;
float HeartRate(){
float H_rate;
return H_rate;
}
void loop(){
H_val = HeartRate();
}