New to C++, modules and switch menu - c++

Question

I am working on a project that involves creating a menu screen, and integrating three programs into one that can be selectively launched from the menu screen.
I thought making individual programs first before piecing them together with switch case and functions would be easy (I don't know class/objects). I keep running into a brick wall and a host of syntax/logical errors, so I deleted everything and now I'm back to square one-- with three distinct programs. This is very daunting-- how do proceed? :/
#include <iostream>
using namespace std;
int main ()
{
int x;
cout << "Enter the amount of money you have ";
cin >> x;
if (x >= 20) {
cout << "You can buy Comic Book $1 or Sports Journal $3 or Science Book $15 or Third Volume Series $20";
} else if (x >= 15 && x < 20) {
cout << "You can buy Comic Book $1 or Sports Journal $3 or Science book $15";
} else if (x >= 3 && x < 15) {
cout << "You can buy Comic Book $1 or Sports Journal $3";
} else if (x >= 1 && x < 3) {
cout << "You can buy Comic Book $1";
} else if (x <= 0) {
cout << "You cannot afford anything";
}
return 0;
}
#include <iostream>
#include <iomanip>
#include <fstream>
using namespace std;
int main()
{
int numclass; //number of classes
int numStudents; //number of students
int numTests; // Number of tests per student
double sectiontotal; //Accumulator for Class total scores
double total; // Accumulator for total scores
double average; //Average test score
double totalaverage = 0;
ofstream outfile;
outfile.open("Gradesinfo.txt");
// Set up numeric output formatting.
cout << fixed << showpoint << setprecision(1);
// Get the number of students.
cout << "This program gives average of test scores per student, per class, and for the whole institution for upto 2 students in upto 2 different classes in 3 subjects\n";
// Determine each student's average score.
cout << "Enter the number of classes";
cin >> numclass;
cout << "Enter the number of students per class";
cin >> numStudents;
cout << "Enter the number of tests";
cin >> numTests;
for (int section = 1; section <= numclass; section++) {
sectiontotal = 0; //Initialize class accumulator
totalaverage = 0;
for (int student = 1; student <= numStudents; student++) {
total = 0; // Initialize the accumulator.
for (int test = 1; test <= numTests; test++) {
double score;
cout << "Enter score " << test << " for ";
cout << "student " << student << ": ";
cin >> score;
if (score >= 0 && score <= 100) {
total += score;
} else {
cout << "Enter value from 1 - 100" << endl;
test = test - 1;
}
}
average = total / numTests;
totalaverage += average;
cout << "The average score for student " << student;
cout << " is " << average << ".\n\n";
outfile << "The average score for student " << student;
outfile << " is " << average << ".\n\n";
}
cout << "The total average for class " << section << " is: " << totalaverage / numStudents << endl;
outfile << "The total average for class " << section << " is: " << totalaverage / numStudents << endl;
sectiontotal += totalaverage;
}
cout << "The total average for the institution is: " << sectiontotal / numclass;
outfile << "The total average for the institution is: " << sectiontotal / numclass;
outfile.close();
return 0;
}
#include<cstdlib>
#include<iostream>
#include<fstream>
using namespace std;
int main()
{
fstream instream;
ofstream outstream;
instream.open("Grades.txt");
if (instream.fail()) {
cout << "The input file failed to open\n";
exit(1);
}
int next, largest, smallest;
largest = 0;
smallest = 0;
while (instream >> next) {
if (largest < next) {
largest = next;
} else {
smallest = next;
}
}
cout << "The highest grade is: " << largest << endl;
instream.close();
system("pause");
return 0;
}

Answer 1

I think you are shooting yourself on the foot. go 1 step after the other, please do take this as reference:
create a main file as entry point for the app, note the prototype and implementation of the functions printA and printB
#include <iostream>
using namespace std;
void printA();
void printB();
int main()
{
int x = 1;
cout << "Enter the option:\n";
while (cin >> x)
{
if (x <= 0)
{
break;
}
switch (x) {
case 1:
printA();
break;
case 2:
printB();
break;
default:
cout << "Invalid";
}
}
return 0;
}
void printB()
{
cout << "B";
}
void printA()
{
cout << "A";
}
create a new file fooA.cpp and paste there the implemented function printA
do the same for the printB in another file.
remove those implementations from main.cpp
you are done!