Loops for assigning/calculating student grade (c++) - c++

Question

I'm sort of having a hard time with my program, and I would really appreciate any help. Forgive me for my really bad code, I'm new.
#include <iostream>
#include <string.h>
using namespace std;
//functions
string getFirstName();
string getLastName();
int getScores();
double calculateSum(double sum, double score);
double calculateAvg(double avg, double sum);
char calculateGrade(double score, char grade);
void displayResults(string firstname, string lastname, double avg, char
grade);
int main(){
//variables
string firstname;
string lastname;
int score;
double sum;
double avg;
char grade;
//functions and parameters
firstname = getFirstName();
lastname = getLastName();
score = getScores();
sum = calculateSum(sum, score);
avg = calculateAvg(avg, sum);
grade = calculateGrade(score, grade);
displayResults(firstname,lastname,avg,grade);
while (true)
{
firstname = getFirstName();
cin >> firstname;
if (firstname == "done")break;
lastname = getLastName();
cin >> lastname;
sum=0.0;
for (int i = 0; i<10; i++)
{
double score;
cin >> score;
sum - calculateSum(sum, score);
sum+=score;
//sum = sum+score;
}
avg = calculateAvg(avg, sum);
avg = sum/10.0;
displayResults(firstname,lastname,avg,grade);
}
return 0;
}
string getFirstName()
{
string firstname;
cout<<"Enter first name: " << endl;
cin >>firstname;
return firstname;
}
string getLastName()
{
string lastname;
cout<<"Enter last name: ";
cin >>lastname;
return lastname;
}
int getScores()
{
int score;
cout <<"Input score: ";
cin >>score;
return score;
}
double calculateSum(double sum, double score)
{
sum+=score;
return sum;
}
double calculateAvg(double avg, double sum)
{
avg = sum/10.0;
return avg;
}
char calculateGrade(double score, char grade)
{
if (score >= 90)
grade = 'A';
else if (score >=80)
grade = 'B';
else if (score >=70)
grade = 'C';
else if (score >=60)
grade = 'D';
else
grade = 'F';
return grade;
}
void displayResults(string firstname, string lastname, double avg, char
grade)
{
cout<<firstname<< lastname<<": "<<avg << grade;
}
I don't really understand loops, or how they work, so what I have written down for my loop was just given to us by our professor, so if anyone could please explain/dissect it then I would really appreciate it! I want to know how to do this, not just have answers handed to me.
So, I'm not sure why my program won't properly execute. I've listed the call functions and all of the functions seem to be correct. My loops are inside of the main as well, but I don't know why they're not working. Also, when I run it, I don't have any errors.
It seems to be stuck on the enter first name and enter last name part, but I'm not sure why.Again, I'd really appreciate any help, thank you!

Answer 1

You code was full of bugs, but I will lead you through it step by step.
First things first, we will need to check what each function does :
1- string getFirstName(); Prompt the user to enter his/her first name. Working
2- string getLastName(); Prompt the user to enter his/her last name. Working
3- int getScores(); Prompt the user to enter his/her score. Working
4- double calculateSum(double sum, double score); Adds both the sum and the score. What you did in your implementation of the function :
{
sum+=score;
return sum;
}
Will only be valid if you pass variable sum by reference. There is no need to get into this now. An easier way to do it is to do so :
{
double add = sum + score;
return add;
}
Next up :
5- double calculateAvg(double avg, double sum); Divides sum by 10 to get the average, there's no need to pass avg as a parameter as that's what we are going to return.
The function should be written as double calculateAvg(double sum);
6- Same goes char calculateGrade(double score, char grade);. There's no need to pass grade. It will be written aschar calculateGrade(double score);.
7- Last one : void displayResults(string firstname, string lastname, double avg, char grade); Working
Ok, now to the main() function :
You'll need to declare all of your variables like so
string firstname;
string lastname;
double score;
double sum ;
double avg ;
char grade;
No need to use our functions here, we are going to use them inside our while loop.
Into the while loop :
There's no need to use cin>> with any of variables cause that's what our functions is doing for us.
When the user enters done as his/her first name exit the loop.
Else, create a for loop that iterates 10 times asking the user to input his/her score, add this score to the sum and then after the for loop ends calculate both the average and the grade and print them out.
The final working version of your code should look like this, if you still have any further questions don't hesitate to ask.
#include <iostream>
#include <string.h>
using namespace std;
//functions
string getFirstName();
string getLastName();
int getScores();
double calculateSum(double sum, double score);
double calculateAvg(double sum);
char calculateGrade(double score);
void displayResults(string firstname, string lastname, double avg, char grade);
int main(){
//variables
string firstname;
string lastname;
double score;
double sum ;
double avg ;
char grade;
while (true)
{
firstname = getFirstName();
if (firstname == "done")
break;
lastname = getLastName();
sum=0.0;
for (int i = 0; i<10; i++)
{
score = getScores();
sum = calculateSum(sum, score); //sum = sum+score;
}
avg = calculateAvg(sum);
grade = calculateGrade(avg);
displayResults(firstname,lastname,avg,grade);
}
return 0;
}
string getFirstName()
{
string firstname;
cout<<"Enter first name: ";
cin >>firstname;
return firstname;
}
string getLastName()
{
string lastname;
cout<<"Enter last name: ";
cin >>lastname;
return lastname;
}
int getScores()
{
int score;
cout <<"Input score: ";
cin >>score;
return score;
}
double calculateSum(double sum, double score)
{
int add = sum + score;
return add;
}
double calculateAvg(double sum)
{
double avg = sum/10.0;
return avg;
}
char calculateGrade(double score)
{
char grade;
if (score >= 90)
grade = 'A';
else if (score >=80)
grade = 'B';
else if (score >=70)
grade = 'C';
else if (score >=60)
grade = 'D';
else
grade = 'F';
return grade;
}
void displayResults(string firstname, string lastname, double avg, char grade)
{
cout<<firstname<< lastname<<" - Average : "<<avg << " - Grade : "<< grade<<endl;
}

Answer 2

The loop is just a way of executing the same piece of code over and over again. By putting code in a loop, you do not have to copy and paste it. Any variable changes which happen during one run through a loop are still present during the next.
In your code:
for (int i = 0; i<10; i++)
{
...
}
is your loop. The "..." is code which will be executed over and over.
The big question which needs to be asked with a loop is: How does a loop know how many times to run your code before it exits?
This is what the:
int i = 0; i<10; i++
is about. Though it looks strange it is actually 3 separate commands. The commands are separated by the semi-colon ';'
int i=0
i<10
i++
Command (1) initialize the loop. You are simply setting the variable i, which an integer, to 0.
Command (2) condition to continue looping. If command (2) is true then the loop will execute (and execute again). Your code is saying execute the loop whilst i is less than 10.
Command (3) calculations executed once per loop. We know in Command (1) that you set i to 0. We know in Command (2) that the loop will run while i is less than 10. 0 is less than 10, so the loop will execute... forever. We don't want this, so during Command (3) we increase i. We count the number of times we run the loop.
So your loop will run 10 times in a row, the code inside it and then exit.