C++ elseif is not printing the right answer

I have a little problem when trying to print the letter-grades. Can anybody lead me int he right direction? I think this is because of all those conditions but i haven't found the glitch yet.

Letter grades are sometimes assigned to numeric scores by using the grading scheme commonly known as grading on the curve. In this scheme, a letter grade is assigned to a numeric score as follows (where m is the mean grade and sd is the standard deviation):

Numeric Score Letter Grade

<m-(sd*1.5) F

between 0.5 and 1.5 * sd below mean D

between 0.5*sd

below and 0.5*sd above mean C

between 0.5 and 1.5*sd above mean B

>1.5*sd above mean A

The mean is the sum of all the scores divided by the number of scores. A simplified formula for standard deviation is:

sqrt((summation(x-m)*2)/n)

Write a program to read in a list of real numbers, representing numeric scores - storing them in a static array, or a dynamic array (created using new), call functions to calculate the mean and standard deviation, and then call a function to calculate and display the letter grade and corresponding numeric score.

#include <iostream>
#include <cmath> 

using namespace std; 

void calculate_mean_sd (int arrcal[], int &num); 
void calculate_and_print_grades (int arrcal[], int num); 

int main (void) 
{
    int arrcal[10], num=0; 
    cout<<"Please enter the number of scores that you'd like to determine the grades for: "; 
    cin>>num; 
    for (int i=0; i<num; i++) 
    {
        cout<<"Please enter a score: "; 
        cin>>arrcal[i]; 
    } 
    calculate_mean_sd (arrcal, num); 
    calculate_and_print_grades (arrcal, num);

    return 0;   
}

void calculate_mean_sd (int arrcal[], int &num) 
{ 
    double mean=0, dSum=0, sum_deviation=0, standard_dev=0; 

    for (int i=0; i<num; i++) 
    { 
        dSum+=arrcal[i]; 
    } 
    mean=dSum/num; 
    cout<<"\n\nMean= "<<mean<<endl; 

    for (int i=0; i<num; i++) 
    { 
        sum_deviation+=(arrcal[i]-mean)*(arrcal[i]-mean);//here is a glitch, I think
    } 

    standard_dev=sqrt(sum_deviation/num); 
    cout<<"Standard deviation= "<<standard_dev<<endl; 
    return; 
}
void calculate_and_print_grades (int arrcal[], int num) 
{ 
    double mean=0, standard_dev=0; 

    char * gradeArray = new char[num]; 
    for (int i=0; i<num; i++) 
    { 
        if (arrcal[i]<(mean-1.5*standard_dev)) 
            cout<<"The letter grade is F.\n"<<gradeArray[i]; 

        else if ((mean-(1.5*standard_dev)) <=arrcal[i] && arrcal[i]<(mean-(0.5*standard_dev)) ) 
            cout<<"The letter grade is D.\n"<<gradeArray[i];
        else if ((mean-(0.5*standard_dev)) <=arrcal[i] && arrcal[i]<(mean+(0.5*standard_dev)) ) 
            cout<<"The letter grade is C.\n"<<gradeArray[i]; 
        else if ((mean+(0.5*standard_dev)) <=arrcal[i] && arrcal[i]<(mean+(1.5*standard_dev)) ) 
            cout<<"The letter grade is B.\n"<<gradeArray[i]; 
        else 
            cout<<"The letter grade is A.\n"<<gradeArray[i]; 
    } 
    return; 
}

If I enter 5 scores, the output will be A even if I enter 70,85,90 and so on.