Inputting Grades with Looping C++ - c++

Question

We're only interested in the #'s in the range [0,100]. There may be number outside the range [0, 100], but they aren't part of our calculation (i.e numbers below 0 and above 100 can be inputted but will be ignored in the calculations and counters).
Assume we assign ABCDF as
[85,100]: A
[75,85): B
[65,75): C
[55,65): D
[0,55): F
For each of the five letter grades, output the number of scores with that grade, and also, if the number of scores wasn't 0, output the average score with that grade. Also, if the number of valid scores (in [0, 100]) wasn't 0, output the average of all the scores
I am having trouble with this looping question. When I input multiple scores, it loops them incorrectly and outputs two sets of grades for each input rather than the example answer shown above. Also I am not sure if my break is placed correctly to exit the program when a word is inputted. Any help will be greatly appreciated!
Here is my code:
#include <iostream>
#include <cmath>
#include <cstdlib>
#include <string>
using namespace std;
int main(){
double scores;
unsigned countA = 0;
unsigned countB = 0;
unsigned countC = 0;
unsigned countD = 0;
unsigned countF = 0;
char grade;
double sumA = 0, sumB = 0, sumC = 0, sumD = 0, sumF = 0;
cout << "Enter scores: ";
for (scores; cin >> scores;){
if (scores > 85 && scores <= 100){
grade = 'A';
countA++;
sumA += scores;
}
else if (scores > 75){
grade = 'B';
countB++;
sumB += scores;
}
else if (scores > 65){
grade = 'C';
countC++;
sumC += scores;
}
else if (scores > 55){
grade = 'D';
countD++;
sumD += scores;
}
else{
grade = 'F';
countF++;
sumF += scores;
}
if (!cin){
break;
}
if (countA == 0){
cout << "# A's: 0 " << endl;
}
else {
cout << "# A's: " << countA << " Average = " << sumA/countA << endl;
} if (countB == 0){
cout << "# B's : 0 " << endl;
}
else{
cout << "# B's: " << countB << " Average = " << sumB /countB << endl;
} if (countC == 0){
cout << "# C's: 0 " << endl;
}
else{
cout << "# C's: " << countC << " Average = " << sumC /countC << endl;
} if (countD == 0){
cout << "# D's: 0 " << endl;
}
else {
cout << "# D's: " << countD << " Average = " << sumD /countD << endl;
} if (countF == 0){
cout << "# F's: 0 " << endl;
}
else {
cout << "# F's: " << countF << " Average = " << sumF /countF << endl;
}
}

Answer 1

TL;DR version: Closing brace on the for loop was missing. Loop never ended and caused OP's output code to also loop.
Long version:
Here is working code. The stuff I changed is marked with comments.
#include <iostream> //removed a bunch of unused includes.
using std::cin; // including all of namespace::std is overkill and often
using std::cout; // leads to hard-to-solve bugs. Only use what you need
using std::endl;
int main()
{
double scores;
unsigned countA = 0;
unsigned countB = 0;
unsigned countC = 0;
unsigned countD = 0;
unsigned countF = 0;
char grade;
double sumA = 0, sumB = 0, sumC = 0, sumD = 0, sumF = 0;
cout << "Enter scores: ";
// for (scores; cin >> scores;){
while (cin >> scores) // cleaner
{
if (scores > 85 && scores <= 100)
{
grade = 'A';
countA++;
sumA += scores;
}
else if (scores > 75)
{
grade = 'B';
countB++;
sumB += scores;
}
else if (scores > 65)
{
grade = 'C';
countC++;
sumC += scores;
}
else if (scores > 55)
{
grade = 'D';
countD++;
sumD += scores;
}
else
{
grade = 'F';
countF++;
sumF += scores;
}
// this test is made redundant by the loop condition
// if (!cin)
// {
// break;
// }
} // this was missing. The loop kept going and included all of
// the following code in the loop.
if (countA == 0)
{
cout << "# A's: 0 " << endl;
}
else
{
cout << "# A's: " << countA << " Average = " << sumA / countA << endl;
}
if (countB == 0)
{
cout << "# B's : 0 " << endl;
}
else
{
cout << "# B's: " << countB << " Average = " << sumB / countB << endl;
}
if (countC == 0)
{
cout << "# C's: 0 " << endl;
}
else
{
cout << "# C's: " << countC << " Average = " << sumC / countC << endl;
}
if (countD == 0)
{
cout << "# D's: 0 " << endl;
}
else
{
cout << "# D's: " << countD << " Average = " << sumD / countD << endl;
}
if (countF == 0)
{
cout << "# F's: 0 " << endl;
}
else
{
cout << "# F's: " << countF << " Average = " << sumF / countF << endl;
}
}

Answer 2

Your question is a bit confusing, I assume your main issue is the output part. Currently your code produces this.
As you see we get intermediate output, after every score entered. To change that the loop needs to be split into two loops: One for input, and one for output that runs after the first:
while (/* we get scores */) {
// update the counters and sums
}
for (/* every score */) {
// print count and average
}
To generate the output in a loop you need to store your data in some "loopable" way. Currently you have multiple local variables. Changing that to an array (indexed by the respective grade) allows us to loop over the data:
unsigned counter[5];
double sum [5];
// A -> 0, B -> 1, ..., F -> 4
for (std::size_t it = 0; it < 5; ++it) {
// use sum[it] and counter[it]
}
But raw arrays (as raw pointers) are evil - only use them when absolutely necessary - we use std::array from the standard library. And to ease iteration and improve logical encapsulation it's good to keep sum and count of each grade together:
struct grade_info {
unsigned count = 0;
double sum = 0;
};
// ... later in the main function
std::array<grade_info, 5> grades;
// input
for (auto const & grade : grades) { // C++11 shorthand to iterate over a collection
// use grade.count and grade.sum
}
Concerning your input:
for (scores; cin >> scores;){
This does the right thing, but is a bit strange. Since scores will only be used inside that loop instead of declaring it as local variable of main we only declare it inside the loop:
for (double score; // only a single score is in that variable at any time
cin >> score; // ends the loop on eof or failure to convert to double (when text got entered)
// no step instructions, the above check does that already
) {
Now there's also no need to test cin inside the loop. The operator>> returns (a reference to) its first argument, which is cin, so the test in the for loop already tests cin, no need for if (! cin) { break; }.
Then you have code like this
grade = 'A';
when you never use the value stored in grade. Just remove that.
Last but not least your input validation isn't working (the 101 in my test case is treated as grade B):
if (scores > 85 && scores <= 100) {
// scores between (85, 100]
}
// scores is either <= 85 OR > 100
else if (scores > 75){
// scores is in (75, 85] OR > 100
}
Ideally you should keep input validation and business logic separated:
if (not input_is_valid(score)) {
continue; // the loop
}
// business logic, assuming valid input
So, the final code could be
#include <iostream>
#include <array>
struct grade_info {
unsigned count = 0;
double sum = 0;
char const name;
grade_info(char n) : name(n) {
}
};
bool input_is_valid(double score) {
return (score >= 0) and (score <= 100);
}
std::size_t score_to_grade_index(double score) {
if (score >= 85) {
return 0;
} else if (score >= 75) {
return 1;
} else if (score >= 65) {
return 2;
} else if (score >= 55) {
return 3;
} else {
return 4;
}
}
int main(int, char**) {
std::array<grade_info, 5> grades {'A', 'B', 'C', 'D', 'F'};
for (double score; std::cin >> score;) {
if (not input_is_valid(score)) {
continue;
}
auto index = score_to_grade_index(score);
++(grades[index].count);
grades[index].sum += score;
}
for (auto const & grade : grades) {
std::cout << "# " << grade.name << ": "
<< grade.count;
if (grade.count > 0) {
std::cout << " avg: " << (grade.sum / grade.count);
}
std::cout << std::endl;
}
return 0;
}
Live here