Error: Expression must have integral or unscoped enum type

Question

#include <iostream>
#include <iomanip>
#include <string>
#include <algorithm>
#include <sstream>

using namespace std;

int main(){

  float size;

  float sumNum = 0;
  float maxNum, minNum;
  float mean;
  float totalDev = 0;
  float devSqr = 0;
  float stdDev;

  //Create a user input size
  std::cout << "How many number would you like to enter? ";
  std::cin >> size;
  float *temp = new float[size];

  //Getting input from the user
  for (int x = 1; x <= size; x++){
    cout << "Enter temperature " << x << ": ";
    cin >> temp[x];
  }

  //Output of the numbers inserted by the user
  cout << endl << "Number --- Temperature" << endl << endl;
  for (int x = 1; x <= size; x++){
    cout << "   " << x << "   ---     " << temp[x] << endl;
    sumNum = sumNum + temp[x];
  }

  //Calculating the Average
  mean = sumNum / size;
  maxNum = minNum = temp[1];

  for (int x = 1; x <= size; x++){
    if (maxNum < temp[x]){
      maxNum = temp[x];
    }
    if (minNum > temp[x]){
      minNum = temp[x];
    }
  }

  //Calculating Sample Standard Deviation
  for (int x = 1; x <= size; x++){
    totalDev = totalDev + (temp[x] - mean);
    devSqr = devSqr + (pow((temp[x] - mean), 2));
  }
  stdDev = sqrt((devSqr / (size - 1)));

  cout << endl << "The sum: " << sumNum << endl; //the sum of all input
  cout << "The mean: " << mean << endl; //calculate the average 
  cout << "Maximum number: " << maxNum << endl; // print biggest value
  cout << "Minimum number: " << minNum << endl; // print smallest value
  cout << "The range between the maximum and the minimum: " << maxNum - minNum << endl; //the range
  cout << "Deviation: " << totalDev << endl;
  cout << "The squares of deviation: " << devSqr << endl;
  cout << "The Standard Deviation: " << setprecision(1) << fixed << stdDev << endl;

  system("pause");
}

I want to get the size of the array from the user, but when I'm using (float *temp = new float[size];), I got an error "expression must have integral or unscoped enum type." When I input the number, it working nicely up until to the range number. After that, start from deviation to the standard deviation, the calculation all messed up.

If I use int for the 'size' and keep the 'temp' as float, it gave me different error.

How can I fix this?

Answer 1

Your variable size is declared as: float size;

You can't use a floating point variable as the size of an array - it needs to be an integer value.

You could cast it to convert to an integer:

float *temp = new float[(int)size];

Your other problem is likely because you're writing outside of the bounds of the array:

   float *temp = new float[size];

    //Getting input from the user
    for (int x = 1; x <= size; x++){
        cout << "Enter temperature " << x << ": ";

        // cin >> temp[x];
        // This should be:
        cin >> temp[x - 1];
    }

Arrays are zero based in C++, so this is going to write beyond the end and never write the first element in your original code.