CGPA the Golden Egg!

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n,m,i,c,t;
    double a,b,sum,cg,cr;
    cin>>n;
    for(i=0;i<n;i++)
    {
        cin>>m;
        sum=0;
        cr=0;
        c=0;
        for(int j=0;j<m;j++)
        {
            cin>>a>>b;
            if(a>=80&&a<=100)
            {
               cg=4.00;
            }
            else if(a>=75&&a<80)
            {
                cg=3.75;
            }
            else if(a>=70&&a<75)
            {
                cg=3.50;
            }
            else if(a>=65&&a<70)
            {
                cg=3.25;
            }
            else if(a>=60&&a<65)
            {
                cg=3.00;
            }
            else if(a>=55&&a<60)
            {
                cg=2.75;
            }
             else if(a>=50&&a<55)
            {
                cg=2.50;
            }
             else if(a>=45&&a<50)
            {
                cg=2.25;
            }
             else if(a>=40&&a<45)
            {
                cg=2.00;
            }
             else if(a<40&&a>=0)
            {
                c++;
            }
            cr+=b;
            sum+=cg*b;
        }
        if(c>0)
        {
            if(c==1)
        cout<<"Case "<<i+1<<": "<<"Sorry, you have failed in "<<1<<" courses!"<<endl;
            else
            cout<<"Case "<<i+1<<": "<<"Sorry, you have failed in "<<c<<" courses!"<<endl;
        }
           else
        {
            cout<<"Case "<<i+1<<": "<<fixed<<setprecision(2)<<sum/cr<<endl;
        }
    }
}

what’s the problem this code?