Thread: Cant figure it out...

I recently took a break from programming(like a month, month an a half maybe). So as a little warmup to get back in the habit of programming, I made this small program. You just chose a category(addition, subtraction, mulitiplication, or division) and then enter 2 numbers. The 2 numbers are manipulated differently, depending on which category you chose. Then it gives you the answer and you go back to the main menu.

Its a really simple program, but for some reason its not working properly. It compiles just fine. But after you select one of the categories it just closes the program. I dont see why though. But I bet its something simple im overlooking.

Code:

#include <iostream>


using namespace std;



void add(){
     
     int x;
     int y;
     int result;
     result = x + y;
     
     cout << " Enter a number: ";
     cin >> x;
     cin.get();
     cout << "\n\n Enter another number: ";
     cin >> y;
     cin.get();
     cout << " " << x << " + " << y << " = " << result;
     cin.get();

     cout << "\n\n\n";
     }
     
void sub(){
     
     int x;
     int y;
     int result;
     result = x - y;
     
     cout << " Enter a number: ";
     cin >> x;
     cin.get();
     cout << "\n\n Enter another number: ";
     cin >> y;
     cin.get();
     cout << " " << x << " - " << y << " = " << result;
     cin.get();

     cout << "\n\n\n";
     }
     
void mult(){
     
     int x;
     int y;
     int result;
     result = x * y;
     
     cout << " Enter a number: ";
     cin >> x;
     cin.get();
     cout << "\n\n Enter another number: ";
     cin >> y;
     cin.get();
     cout << " " << x << " * " << y << " = " << result;
     cin.get();

     cout << "\n\n\n";
     }
     
void div(){
     
     int x;
     int y;
     int result;
     result = x/y;
     
     cout << " Enter a number: ";
     cin >> x;
     cin.get();
     cout << "\n\n Enter another number: ";
     cin >> y;
     cin.get();
     cout << " " << x << " / " << y << " = " << result;
     cin.get();

     cout << "\n\n\n";
     }
     
                            
int main(){
    
    int lesson;
     
     cout << "\n\n\n";
     cout << " Welcome to Math Fun Lessons 1 - 4 \n\n\n";
     cout << " Please select a lesson.\n\n";
     cout << " 1. Addition \n";
     cout << " 2. Subtraction \n";
     cout << " 3. Multiplication \n";
     cout << " 4. Division \n\n";
     cout << " Lesson: ";
     cin >> lesson;
     if(lesson == 1){
               cout << "\n\n";
               void add();
               }
     else if(lesson == 2){
          cout << "\n\n";
          void sub();
          }
     else if(lesson == 3){
          cout << "\n\n";
          void mult();
          }
     else if(lesson == 4){
          cout << "\n\n";
          void div();
          }
     else{
          cout << " Invalid Syntax. Try again.\n\n";
          }
    }

Where the IF statement is at the end, that was originally a switch case. But since it wasnt working I figured I did the switch case incorrectly, so I changed it to an IF.

Also, you seem to have become confused about the idea of an expression - take this piece:

Code:

void add(){
     
     int x;
     int y;
     int result;
     result = x + y;

That red line calculates the sum of x and y, and stores the answer in result, based on the current values of x and y - it does not automatically update the result at any time after this line of code, i.e. when you enter values for x and y. You need to move this line to after the lines where you read in values and then print the result. You'll have to do that for each of your functions.

>>It compiles just fine.

You need to turn up the warning level on your compiler - you should get warnings about x and y being used before being initialised - x and y are not guaranteed to be any value, and will probably contain whatever junk value was in that memory location before the program started.

> You need to turn up the warning level on your compiler - you should get warnings about x and y being used before being initialised

Not with g++ 3.4.5 (MinGW)

Also, when calling functions you simply write:

Code:

 
if(lesson == 1)
{
   cout << "\n\n";
   add();
}

rather than

Code:

 
if(lesson == 1)
{
   cout << "\n\n";
   void add();
}

If you do the second as you are doing it never calls the function.

--------------------------------------------------------------------
Also, not sure if you know, but you can have functions accept values and return values to simplify 'em and reduce code redundancy, which may result in more errors and difficulty changing your code at a later time. Of course this isn't necessary as your code should work just as well as is. Just providing an alternative example.

Ex:

Code:

#include <iostream>

using namespace std;

int add(int x, int y)
{
  return x + y;
}

int sub(int x, int y)
{
  return x - y;
}

int mult(int x, int y)
{
  return x * y;
}

int div(int x, int y)
{
  return x / y;
}
                            
int main()
{
  int lesson;
  int x, y;
     
  cout << "\n\n\n";
  cout << " Welcome to Math Fun Lessons 1 - 4 \n\n\n";
  cout << " Please select a lesson.\n\n";
  cout << " 1. Addition \n";
  cout << " 2. Subtraction \n";
  cout << " 3. Multiplication \n";
  cout << " 4. Division \n\n";
  cout << " Lesson: ";
  
  cin >> lesson;
       
  cout << " Enter a number: ";
  cin >> x;
  cin.get();
  cout << "\n\n Enter another number: ";
  cin >> y;
  cin.get();
  cout << "\n\n\n";
     
  if(lesson == 1)
  {
    cout << " " << x << " + " << y << " = " << add(x, y);
  }
  else if(lesson == 2)
  {
   cout << " " << x << " - " << y << " = " << sub(x, y);
  }
  else if(lesson == 3)
  {
   cout << " " << x << " * " << y << " = " << mult(x, y);
  }
  else if(lesson == 4)
  {
   cout << " " << x << " / " << y << " = " << div(x, y);
  }
  else
  {
   cout << " Invalid Syntax. Try again.\n\n";
  }
}

I figured it was something pretty simple.

Richie T, the reason I have it like that is because Ive used( result = x + y; ) before and it worked. Wel, worked in that spot.

>>>If you do the second as you are doing it never calls the function.

I have to do the second one. I get erros when I do it without the void.


And about the alternative you suggested. That was my original idea but I couldnt remember how to do it lol(ive only used that format like 2-3 times before). Oh, and its all better now. Thanks.

>I have to do the second one. I get erros when I do it without the void.
Then you've got something else wrong.

Next you should add a differentiation and calculus lesson

Sorry, I am differentiatingly mad at the mo as I am doing it in school at the moment.