Arduino addition assignment - c++

Question

I do some programming using Arduino, but I have a problem. In the loop() function I want to add a value to a variable, pwm, each time the loop() function is executed. I obtain that value from some function I wrote and add it to pwm with the command pwm += result, but it does not work. If I print pwm, I always get zero. Even though printing result gives me some non-zero value. The whole code is:
float pwm = 0;
float result = 0;
void loop(){
....
errV = w - cm;
errDtV = errOldV - errV;
result = flc->cog(errV, errDtV);
Serial.print("RESULT: ");
Serial.println(result);
pwm += result;
Serial.println(pwm);
}
And the output is like this:
RESULT: 31.98
0.00
What might be wrong?
EDIT: Here is the whole sketch
#include "FSet.h"
#include "FRule.h"
#include "Flc.h"
#include <NewPing.h>
#include "MotorControl.h"
MotorControl* m;
Flc* flc;
FRule* rule1,*rule2,*rule3,*rule4,*rule5,*rule6,*rule7,*rule8,*rule9;
NewPing sonar1(32,33,200);
static int dirA = 9;
static int pwmA = 8;
// Setup the FSets
FSet errZ(0,5,0);
FSet errMP(-15,15,0);
FSet errLP(-30,15,-1);
FSet errDtLN(-4,2,-1);
FSet errDtMN(-2,2,0);
FSet errDtZ(0,2,0);
FSet errDtMP(2,2,0);
FSet errDtLP(4,2,1);
FSet cntLN(-40,20,0);
FSet cntMN(-20,20,0);
FSet cntZ(0,20,0);
FSet cntMP(20,20,0);
FSet cntLP(40,20,0);
void setup(){
Serial.begin(4800);
pinMode(dirA,INPUT);
//Creating FRules for test
rule1 = new FRule(&errZ,&errDtMP,&cntMN);
rule2 = new FRule(&errZ,&errDtZ,&cntZ);
rule3 = new FRule(&errZ,&errDtMN,&cntMP);
rule4 = new FRule(&errMP,&errDtLP,&cntMN);
rule5 = new FRule(&errMP,&errDtMN,&cntMP);
rule6 = new FRule(&errLP,&errDtMP,&cntMP);
rule7 = new FRule(&errLP,&errDtZ,&cntLP);
rule8 = new FRule(&errLP,&errDtMN,&cntLP);
rule9 = new FRule(&errLP,&errDtLN,&cntLP);
flc = new Flc(9);
flc->addRule(rule1);
flc->addRule(rule2);
flc->addRule(rule3);
flc->addRule(rule4);
flc->addRule(rule5);
flc->addRule(rule6);
flc->addRule(rule7);
flc->addRule(rule8);
flc->addRule(rule9);
}
int errV = 0;
int errOldV = 0;
int errDtV = 0;
int w = 30;
unsigned int uS;
unsigned int cm;
float pwm1 = 0;
float result = 0;
void loop(){
uS = sonar1.ping();
cm = (uS / US_ROUNDTRIP_CM);
errV = w - cm;
errDtV = errOldV - errV;
result = flc->cog(errV,errDtV);
Serial.print("RESULT: ");
Serial.println(result);
pwm1 = pwm1 + result;
Serial.println(pwm1);
analogWrite(pwmA,pwm1);
errOldV = errV;
}
FLC class header file:
#ifndef FLC_H
#define FLC_H
#include "Arduino.h"
#include "FRule.h"
class Flc {
public:
Flc(int size);
~Flc();
int addRule(FRule* rule);
int mom(float x1,float x2);
float cog(float x1,float x2);
FRule** rules;
private:
int last;
int size;
float h;
float numerator = 0;
float denominator = 0;
float result = 0;
};
#endif
FLC class source:
#include "Arduino.h"
#include "Flc.h"
Flc::Flc(int size){
this->rules = (FRule**) malloc(sizeof(FRule*) * size);
this->size = size;
last = -1;
}
Flc::~Flc(){
free(rules);
}
int Flc::addRule(FRule* rule){
this->rules[++last] = rule;
return last;
}
int Flc::mom(float x1,float x2){
return 0.0;a
}
float Flc::cog(float x1, float x2){
for(int i = 0; i < size;i++){
h = rules[i]->dof(x1,x2);
float area = rules[i]->widthOfCon() * ( h - h*h/2);
numerator += rules[i]->cntrOfCon() * area;
denominator += area;
}
result = numerator / denominator;
return result;
}

Answer 1

Something in your function cog() is stomping on the variable pwm. Once the float variable is corrupt, Serial.print() will just show zero. The sample below shows that with the float set to 0xffffff, the floating point math library stops making any operation on the variable.
Run the sample program below and you will see that one time pwm prints correctly. After the first bad call, it prints zeros. Also the memory occupied no longer changes.
pwm=0.50 zpwm=0.50
pwm=0.00 zpwm=3.95 result=3.45
255-255-255-255
pwm=0.00 zpwm=4.45
pwm=0.00 zpwm=7.90 result=3.45
255-255-255-255
Sample program showing a function that writes to wrong memory location.
Looking at the memory map output by the linker, the variables are placed in memory in the order listed. So writing past the end of var, will corrupt pwm.
float zpwm = 0;
byte var = 0;
float pwm = 0;
float result = 0;
float badactor() {
*((long*)(&var+1)) = -1;
return 3.45;
}
void setup() {
Serial.begin(57600);
}
void loop() {
zpwm += 0.5;
pwm += 0.5;
Serial.print("pwm=");
Serial.print(pwm);
Serial.print(" zpwm=");
Serial.println(zpwm);
result = badactor();
pwm += result;
zpwm += result;
Serial.print("pwm=");
Serial.print(pwm);
Serial.print(" zpwm=");
Serial.print(zpwm);
Serial.print(" result=");
Serial.println(result);
uint8_t* ptr;
ptr = (uint8_t*)&pwm;
Serial.print((int)*(ptr));
Serial.print("-");
Serial.print((int)*(ptr+1));
Serial.print("-");
Serial.print((int)*(ptr+2));
Serial.print("-");
Serial.println((int)*(ptr+3));
delay(1000);
}