# Rewrite an array with for

``````float y = {1, 0.95, 0.85, 0.76, 0.71, 0.65, 0.52, 0.43, 0.32, 0.22, 0.11};

void setup(){
Serial.begin(9600);
delay(200);

for(int i=0; i<11; i++){
y[i]=-log10(y[i]/y);
Serial.println(y[i]);
}
``````

I'm trying to rewrite the y[i] using for but isnt working, how can I do this properly?

Full code:

``````// EXEMPLO - http://en.wikipedia.org/wiki/Simple_linear_regression

float x = {0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1};
float y = {1, 0.95, 0.85, 0.76, 0.71, 0.65, 0.52, 0.43, 0.32, 0.22, 0.11};
float lrCoef = {0, 0};

// INICIANDO AS VARIÁVEIS
float sum_x = 0;
float sum_y = 0;
float sum_xy = 0;
float sum_xx = 0;

void setup(){
Serial.begin(9600);
delay(200);

for(int i=0; i<11; i++){
y[i]=-log10(y[i]/y);
Serial.println(y[i]);
}

// CHAMA O ALGORITMO DE REGRESSÃO LINEAR
simpLinReg(x, y, lrCoef, 11);
Serial.println("Equação Linear:");
Serial.println("");
Serial.print("Abs = ");
Serial.print(lrCoef, 11);

if (lrCoef > 0){
Serial.print("*Conc + ");
}
else{
Serial.print("*Conc ");
}

Serial.println(lrCoef, 4);
}

void loop(){
}

void simpLinReg(float* x, float* y, float* lrCoef, int n){
// CALCULOS PARA REGRESSÃO LINEAR
for (int i=0; i<n; i++){
sum_x += x[i];
sum_y += y[i];
sum_xy = sum_xy+x[i]*y[i];
sum_xx = sum_xx+x[i]*x[i];
}
lrCoef=(n*sum_xy-sum_x*sum_y)/(n*sum_xx-sum_x*sum_x);
lrCoef=(sum_y/n)-((lrCoef*sum_x)/n);
}
``````

Tells us nothing, except that you are unhappy.

What did you expect to happen and what happens instead?

The problem is with this part of the code

`````` for(int i=0; i<11; i++){
y[i]=-log10(y[i]/y);
Serial.println(y[i]);
}
``````

When I run the code with this for this happens

But if I remove the for all works well. What I'm trying to do is to convert the y[i] for y[i]=-log10(y[i]/y). But I think the problem is with the y that I want to fix in this line code

The first entry you replace is `y`. Perhaps you should save that value first:

``````  float y0 = y;
for(int i=0; I < 11; i++)
{
y[i] = -log10(y[i]] / y0);
Serial.println(y[i]);
}
``````
1 Like

What is log10(1), and what happens when you divide any nnumber by log10(1)?

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