I am trying to add two float arrays into a third array but receive only zeros-CodePudding

I want to use 3 looping structures for three different arrays. The first loop generates numbers 0 to 49. The second loop takes the first loop numbers and squares them. The third loop holds the sum of all 49 values.

If I put it all in a single statement, I get exactly what I want, except it doesn't fill each array:

System.out.println(value[i]   "\t"   Math.pow(value[i], 2)   "\t"   (value[i]   Math.pow(value[i], 2)));

I'm having troubles with the code. After using print statements, I can see the first loop working, however it isn't filling the second loop which is resulting in all zeros.

int loopMax = 49;
value = new float [50];
valueSQ = new float [50];
sum = new float [value.length   valueSQ.length];

for (i = 0; i < loopMax; i  )
{
    value[i] = i   1;
}

/*Results in 49 zeros*/
for (j = 0; j < loopMax; j  )
{
    valueSQ[j] = (float) Math.pow(value[i], 2);
    //System.out.println (valueSQ[j]);
}

/*Results in all zeros*/
for (k = 0; k < loopMax; k  )
{
    sum[k] = valueSQ[j]   value[i];
    System.out.println (sum[k]);
}

This is my base code. I figured the zeros were because I wasn't filling the second array properly. I tried creating new arrays since I can't change the old arrays but it hasn't helped. Could someone explain to me what I am doing wrong or why I'm getting all zeros after the first loop?

CodePudding user response：

sum[k] = valueSQ[j]   value[i];

The values j and i are not what you need them to be.

Change the above line in:

sum[k] = valueSQ[k]   value[k];

EDIT: as @SagunDevkota already stated, in your second loop,

change:

valueSQ[j] = (float) Math.pow(value[i], 2);

valueSQ[j] = (float) Math.pow(value[j], 2);

The reason for this is because i is not reset for the second loop, nor will it augment, the way j will.

You should consider i to be out of scope for the second and third loop, and j for the third loop.

As @JonSkeet remarked, it is better to declare the variable where you need them in such cases:

        for (i = 0; i < loopMax; i  )     {
            value[i] = i   1;
        }
        
        for (j = 0; j < loopMax; j  ){
            valueSQ[j] = (float) Math.pow(value[i], 2);
        }

This shows us that both i and j are declared as instance variables, static variables, or earlier in the method this code is from.

If you remove those variables, and re-write the code like this:

        for (int i = 0; i < loopMax; i  )     {
            value[i] = i   1;
        }
        
        for (int j = 0; j < loopMax; j  ){
            valueSQ[j] = (float) Math.pow(value[i], 2);
        }

When you try to compile this, the compiler will tell you that you are using i out of it's scope. The variable i only exists within the scope of the first loop, so the code for the second loop would not compile.

CodePudding user response：

Change value[i] to value[j] in second loop

valueSQ[j] = (float) Math.pow(value[j], 2);

Change valueSQ[j] to valueSQ[k] and value[i] to value[k] in third loop

sum[k] = valueSQ[k]   value[k];