How to write functions and call them from main [closed] - c++

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#include<iostream>
#include<iomanip>
#include<string>
#include<fstream>
using namespace std;
struct studentType
{
string studentFName[20];
string studentLName[20];
string studentData[20][3];
int testscore[20][5];
char grade[20];
};
studentType s;
int main()
{
int index;
int maxindex;
int maxindex1;
int coldex;
int coldex1;
int totalscore[20];
double avscore[20];
double highscore;
double highindivscore;
maxindex = 0;
maxindex1 = 0;
coldex1 = 0;
ifstream infile;
infile.open("test.txt");
for(index = 0; index < 20; index++)
{
infile >> s.studentFName[index] >> s.studentLName[index] >> s.testscore[index][0] >> s.testscore[index][1] >> s.testscore[index][2] >> s.testscore[index][3] >> s.testscore[index][4];
totalscore[index] = ((s.testscore[index][0]) + (s.testscore[index][1]) + (s.testscore[index][2]) + (s.testscore[index][3]) + (s.testscore[index][4]));
avscore[index] = (static_cast<double>(totalscore[index])/5);
if(avscore[index]<= 100)
{
s.grade[index] = 'A';
}
if(avscore[index]<= 89.9)
{
s.grade[index] = 'B';
}
if(avscore[index]<= 79.9)
{
s.grade[index] = 'C';
}
if(avscore[index] <= 69.9)
{
s.grade[index] = 'D';
}
if(avscore[index] <= 59.9)
{
s.grade[index] = 'F';
}
}
for (index = 0; index < 20; index++)
{
cout << s.studentLName[index] << "," << " " << s.studentFName[index] << " " << s.testscore[index][0] << " " << s.testscore[index][1] << " " << s.testscore[index][2] << " " << s.testscore[index][3] << " " << s.testscore[index][4] << " " << s.grade[index] << endl;
}
cout << endl;
for (index = 1; index < 20; index++)
for (coldex = 0; coldex < 5; coldex++)
{
if (s.testscore[maxindex1][coldex1] < s.testscore[index][coldex])
{
maxindex1 = index;
coldex1 = coldex;
}
}
highindivscore = s.testscore[maxindex1][coldex1];
for (index = 1; index < 20; index++)
{
if (avscore[maxindex] < avscore[index])
{
maxindex = index;
}
}
highscore = avscore[maxindex];
cout << s.studentFName[maxindex] << " " << s.studentLName[maxindex] << " Achieved The Highest Average Test Score Of A: " <<highscore <<endl;
cout << s.studentFName[maxindex1] << " " << s.studentLName[maxindex1] << " " << s.testscore[maxindex1][coldex1] << endl;
infile.close();
system("pause");
return 0;
}
here is the homework question, i know i did it wrong which is why i need help. How do i make main function calls. I am new to this. I have this lab that's got me stumped. The assignment reads (emphasis mine):
Write programs for the following and test to make sure they work. Please follow the book’s guidelines or my style guidelines to write code. Write a program that reads students’ names followed by their test scores from the given input file. The program should output to a file, output.txt, each student’s name followed by the test scores and the relevant grade.. Student data should be stored in a struct variable of type StudentType, which has four components: studentFName and studentLName of type string, testScore of type int and grade of type char. Suppose that the class has 20 students. Use an array of 20 components of type StudentType. Your program must contain at least the following functions:
A function to read the students’ data into an array.
A function to assign the relevant grade to each student.
Your program should output each student’s name in this form: last name followed by a comma, followed by a space, followed by the first name; the name must be left justified. Moreover, other than declaring the variables and opening the input and output files, the function main should only be a collection of function calls.

Answer 1

This is called refactoring. I guess for the assignment you want to move everything that is in main into individual functions. You could just cut and paste the whole body of main and move it to one function and call it in main. I don't really think that is the point of the assignment though.
Instead, read over main and separate/extract procedures. You should separate main into functions that do one thing i.e. handle input/output, loop, check some variable and return a letter, etc. These kind of changes not only make the program much easier to understand and come back to later, but also make it much easier to reuse procedures that are repeated throughout the program.

Answer 2

Your code looks fine logically and should work, however, what your homework is asking of you is to essentially code with good style and separate the sections of the program into functions.
Essentially, as an easy fix, just place different sections that do similar things from the code into void functions. For example, this cpp segment:
void function1();
void function2();
void function3();
void main(){
function1();
function2();
function3();
return 0;
}
void function1(){
// Your code. Ex: Some large algorithm.
}
void function2(){
//More code, for a different algorithm. Maybe some input or output.
}
void function3(){
//The final code you want the program to execute.
}
And then pass parameters and adjust return types as needed. It makes the code easier to follow, especially if you have the functions named after what they do such as gradingLogic() or studentOutput().