program doesnt increment right

[LATCH100]

so there is suppose to be a constant that shows the total number of values to be shown in this range. The user enters two values, lets say userMin is -2 and userMax is 2, it's suppose to add 0.2 to -2 and so on until it reaches 2. It starts doing that up until it reaches -1.0, then it goes to -0.9, -0.7.... etc, It also goes beyond 2, which i think is because the incrementation is wrong. Any ideas?

#include <iostream> 
#include <iomanip>

using namespace std;

int main()
{

   cout << fixed << setprecision(1);
   float userMin;
   float userMax;
  
   const int SIZE = 21;
   float arr[SIZE];
   const int SIZE2 = 21;
   float arr2[SIZE2];
   int count = 0;
   cout << "enter min ";
   cin >> userMin;
   cout << "enter max ";
   cin >> userMax;
   float inc = (userMax-userMin)/SIZE;
   float x = inc*count + userMin;



   while (x <= userMax)
   {
      for (int e = 0; e < SIZE; e++)
      {
         arr[e] = x;
         arr2[e] = 2 * x*x*x + 4 * x + 5;
         cout << setw(15) << arr[e]
            << setw(15) << arr2[e]
            << endl;

         count++;
         x = userMin + inc*count;
      }
   }

   return 0;
}

 -2.0      -19.0
   -1.8      -14.1
   -1.6      -10.0
   -1.4      -6.5
   -1.2      -3.7
   -1.0      -1.5
   -0.9       0.3
   -0.7       1.7
   -0.5       2.9
   -0.3       3.8
   -0.1       4.6
    0.1       5.4
    0.3       6.2
    0.5       7.1
    0.7       8.3
    0.9       9.7
    1.0       11.5
    1.2       13.7
    1.4       16.5
    1.6       20.0
    1.8       24.1
    2.0       29.0
    2.2       34.8
    2.4       41.5
    2.6       49.3
    2.8       58.2
    3.0       68.3
    3.1       79.7
    3.3       92.4
    3.5       106.6
    3.7       122.3
    3.9       139.7
    4.1       158.7
    4.3       179.6
    4.5       202.3
    4.7       226.9
    4.9       253.6
    5.0       282.4
    5.2       313.4
    5.4       346.7
    5.6       382.3
    5.8       420.4

[disturbedfuel15]

I would explore why when you put in 20 for your size, and change "while" to "if", it performs correctly.

[LATCH100]

can you explain why that happens with 20 instead of 21. i also put a break in the nested loop to stop it at 2. if i dont itll keep going past it.
Edit: the constant has to match up with the total number of values

[disturbedfuel15]

Don't count the min size value.

[dhayden]

You don't need the while loop at line 27 at all. If you remove that you get this output:

$ ./foo
enter min -2
enter max 2
           -2.0          -19.0
           -1.8          -14.1
           -1.6          -10.0
           -1.4           -6.5
           -1.2           -3.7
           -1.0           -1.5
           -0.9            0.3
           -0.7            1.7
           -0.5            2.9
           -0.3            3.8
           -0.1            4.6
            0.1            5.4
            0.3            6.2
            0.5            7.1
            0.7            8.3
            0.9            9.7
            1.0           11.5
            1.2           13.7
            1.4           16.5
            1.6           20.0
            1.8           24.1

Looks close, but is it really? Let's comment out line 9. Don't remove it - we'll put it back later. Here is the output with line 9 commented out:

$ ./foo
enter min -2
enter max 2
             -2            -19
       -1.80952       -14.0882
       -1.61905       -9.96426
       -1.42857       -6.54519
        -1.2381       -3.74808
       -1.04762       -1.49001
      -0.857143       0.311954
      -0.666667        1.74074
       -0.47619        2.87928
      -0.285714         3.8105
     -0.0952381        4.61732
      0.0952381        5.38268
       0.285714         6.1895
       0.476191        7.12072
       0.666667        8.25926
       0.857143        9.68805
        1.04762          11.49
         1.2381        13.7481
        1.42857        16.5452
        1.61905        19.9643
        1.80952        24.0882

Well that ain't right. The x should increase by 0.2. Small rounding errors won't account for these large differences so something is clearly wrong with the increment value. Looking at the code I see a fence post problem. If you divide the range from -2 to 2 into intervals 0.1 wide, then you get 21 values, but only 20 intervals. So let's change line 22 to
float inc = (userMax-userMin)/(SIZE-1);

$ ./foo
enter min -2
enter max 2
             -2            -19
           -1.8        -13.864
           -1.6         -9.592
           -1.4         -6.088
           -1.2         -3.256
             -1             -1
           -0.8          0.776
           -0.6          2.168
           -0.4          3.272
           -0.2          4.184
    2.98023e-08              5
            0.2          5.816
            0.4          6.728
            0.6          7.832
            0.8          9.224
              1             11
            1.2         13.256
            1.4         16.088
            1.6         19.592
            1.8         23.864
              2             29

Much better! The highlighted value might appear wrong, but it's really just a number very close to zero. If you uncomment line 9 you'll get the right output:

$ ./foo
enter min -2
enter max 2
           -2.0          -19.0
           -1.8          -13.9
           -1.6           -9.6
           -1.4           -6.1
           -1.2           -3.3
           -1.0           -1.0
           -0.8            0.8
           -0.6            2.2
           -0.4            3.3
           -0.2            4.2
            0.0            5.0
            0.2            5.8
            0.4            6.7
            0.6            7.8
            0.8            9.2
            1.0           11.0
            1.2           13.3
            1.4           16.1
            1.6           19.6
            1.8           23.9
            2.0           29.0

[LATCH100]

wow thanks , we must have commented at the same time so i didnt see your post until now. thanks again