functions and arrays to calculate gpa - c++

Question

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This is what I have tried out but whenever I run the program it crashes and says error, although it compiles correctly. It asks me to enter department number but after that doesn't show me any output
#include <iostream>
#include <cstdlib>
#include <iomanip>
using namespace std;
const int STDTs = 25;
const int DEPTs = 7;
void initializeGPAs(double gpa[][DEPTs])
{
for(int i=0;i<STDTs;i++)
for(int j=0;j<DEPTs;j++)
gpa[i][j]=(10+rand()%31)/10;
}
void computeDeptAvg(double gpa[][DEPTs] , double deptAvg[])
{
for(int i=0;i<STDTs;i++)
{
int sum=0;
for(int j=0;j<DEPTs;j++)
sum+=gpa[j][i];
deptAvg[i]=double(sum/STDTs);
}
}
int StdsOnProbationCount(double gpa[][DEPTs])
{
int ctr=0;
for(int i=0;i<STDTs;i++)
for(int j=0;j<DEPTs;j++)
if(gpa[i][j]<2)
ctr++;
return ctr;
}
int StdsOnProbationCountinDeptX(double gpa[][DEPTs], int x)
{
int ctr=0;
for(int i=0;i<STDTs;i++)
if(gpa[i][x-1]<2)
ctr++;
return ctr;
}
void showReport(double gpa[][DEPTs],string dept_names[], double deptAvg[], int ctr1, int ctr2, int x)
{
cout<<endl;
for(int i=0;i<DEPTs;i++)
{
cout<<'\t'<<dept_names[i]<<" ";
}
cout<<endl;
for(int i=0;i<STDTs;i++)
{
cout<<"Student "<<i+1<<": ";
for(int j=0;j<DEPTs;j++)
cout<<gpa[i][j]<<" ";
cout<<endl;
}
cout<<endl;
for(int t=0;t<DEPTs;t++)
cout<<"Dept Avg.: "<<deptAvg[t]<<" ";
cout<<endl<<endl;
cout<<"Total number of students who are on probation is: "<<ctr1;
cout<<endl;
cout<<"Number of students who are on probation in "<<dept_names[x-1]<<" Dept. is "<<ctr2;
}
int main()
{
double gpa[STDTs][DEPTs];
int ctr1, ctr2, x;
double deptAvg[DEPTs];
string dept_names[DEPTs]={"MATH","STAT","COMP","PHYS","CHEM","BIOL","GEOL"};
initializeGPAs(gpa);
computeDeptAvg(gpa, deptAvg);
ctr1 = StdsOnProbationCount(gpa);
cout<<"Enter Department Number [1 to 7]: ";
cin >> x;
ctr2 = StdsOnProbationCountinDeptX(gpa, x);
showReport(gpa, dept_names, deptAvg, ctr1, ctr2, x);
return 0;
}
edit: I figured everything out but my problem seems to be in this function because it displays zeroes for all the department averages
void computeDeptAvg(double gpa[][DEPTs] , double deptAvg[])
{
for(int i=0;i<STDTs;i++)
{
int sum=0;
for(int j=0;j<DEPTs;j++)
{
sum+=gpa[j][i];
deptAvg[j]=double(sum/STDTs*1.0);
}
}
}

Answer 1

I'll consider only your computeDeptAvg function.
Your sum variable should be of type double, declaring it as an int makes all of your calculations (specifically the sum+=gpa[j][i] and sum/STDTs, which is an integer division) prone to truncating errors.
You nested the two loops in the wrong order: You should sum the scores of all the students in a particular department in order to calculate the average of that department. Besides, deptAvg[j] is overwritten every time the outer loop is executed.
You have declared gpa in main as a double gpa[STDTs][DEPTs];, but in your loops you are using gpa[j][i], where j is in the range [0, DEPTs) and i in [0, STDTs).
A modified version could be:
void computeDeptAvg(double gpa[][DEPTs] , double deptAvg[])
{
for(int d = 0; d < DEPTs; d++)
{
double sum = 0.0;
for(int s = 0; s < STDTs; s++)
{
sum += gpa[s][d];
}
deptAvg[d] = sum / STDTs;
}
}