Question

#include<iostream>
using namespace std;

int main()
{

float num,avg,sum=0.0;
int count=0;
bool moreNumbers=true;

cout<<"Enter grades:"<<endl;
while(moreNumbers)
{
cin>>num;
if(num < 0)
{
moreNumbers=false;
}
else
{
count = count+1;
sum=sum+num;
}
}
avg=sum/count;

cout<<"Average grade:"<<avg<<endl;
cout<<"How many grades were entered:"<<count<<endl;
return 0;
}

Question: We need to add another loop to check input. Just like the input loop we already have, this one should use a boolean variable as a control. So, the logic could be something like this:

Loop
 Prompt user for a number
 If number is valid set flag variable to true else set flag variable to false
 Continue loop while flag variable is false

Answer 1

#include<iostream>/*Use Dev C++*/
using namespace std;
int main()
{
float avg,sum=0.0;
int count=0;
bool moreNumbers=true;
bool ans=true;
char ch,ch1;
int g;
bool flag=true;
while(ans)
{
flag=true; /*re initialization of variables */
count=0;
avg,sum=0.0;
  
while(flag)
{cout<<endl;
    cout<<"Enter grades: "<<endl;
cin>>g;
if(g<0)
{
cout<<"Invalid Number";
exit(0);       }   
    sum=sum+g;
       count=count+1;
       cout<<"More grades ?(y/n)";
       cin>>ch1;
       if (ch1=='y'||ch1=='Y')
       flag=true;
       else
       flag=false; }
avg=sum/count;
cout<<"Average grade:"<<avg<<endl;
cout<<endl;
cout<<"How many grades were entered:"<<count<<endl;
cout<<endl;
cout<<"Do you want to repeat...(y/n)";
cin>>ch;
if (ch=='y' || ch=='Y')   
    ans=true;
else
ans=false;}
return 0;
}