Thread: Problems with a menu

I recommend you declare just 2 ints, a and b, and do so just after the opening braces in main(). Then in each case option obtain user input into a and b and pass a and b to the desired funtion. Function calls are made by typing the name of the function and the parameters to be sent, such as add(a, b); or subt(a, b). A function call should not have any type information in it like the declaration and first line of the definition need.

Here's your latest post of code with a few comments outlining
what you did wrong:

Code:

#include <iostream>

//Dont need these 3 because you dont use any functions from them
#include <cstdio>
#include <cstdlib> 
#include <string> 

using namespace std;

int selection;				//You should declare this inside main
int mult (int a,int b);
int divi (int c,int d);
int add (int e,int f);
int subt (int g,int h);

int main()
{
    cout<<"1. Multiplication";	//These are probably printing all on the same line - use cout << endl
    cout<<"2. Division";	//to move to next line
    cout<<"3. Addition";
    cout<<"4. Subtraction";
    cout<<"5. Exit";
    cin>> selection;
    cin.ignore();
    
    switch (selection)
{	//Watch your braces - its a style issue - not critical
    case 1:
             int mult (int a,int b);	//Here is your problem - the stuff that
             int a;			//the function is supposed to do 
             int b;			//shouldn't be here - it should
         {				//be defined outside main
             cout<<"Please input two numbers to be multiplied: ";
             cin>> a >> b;
             cin.ignore();
             cout<<"The product of your two numbers is "<< mult (a,b) <<".\n";
             cin.get();
         }
         int mult (int a,int b);
         {
             return a*b;
         }
         break;
    case 2:
         int divi (int c,int d);		//As above
         int c;
         int d;
         {
             cout<<"Please input two numbers to be divided: ";
             cin>> c >> d;
             cin.ignore();
             cout<<"The product of your two numbers is "<< divi (c,d) <<".\n";
             cin.get();
         }
         int divi (int c,int d);
         {
             return c/d;
         }
         break;
    case 3:
         int add (int e,int f);		//As above
         int e;
         int f;
         {
             cout<<"Please input two numbers to be added: ";
             cin>> e >> f;
             cin.ignore();
             cout<<"The product of your two numbers is "<< add (e,f) <<".\n";
             cin.get();
         }
         int add (int e,int f);
         {
             return e+f;
         }
         break;
    case 4:
         int subt (int g,int h);	//Once again, as above
         int g;
         int h;
         {
             cout<<"Please input two numbers to be subtracted: ";
             cin>> g >> h;
             cin.ignore();
             cout<<"The product of your two numbers is "<< subt (g,h) <<".\n";
             cin.get();
         }
         int subt (int g,int h);
         {
             return g-h;
         }
         break;
    case 5:
         return 0;
}
}

Now here is your corrected code - this compiles now:

Code:

#include <iostream>

using namespace std;

int mult (int a,int b);
int divi (int a,int b);
int add (int a,int b);
int subt (int a,int b);

int main()
{
	int selection;	
	int a;			//You won't need different variables for each function	
        int b;			//These to are used for all operations

    cout<<"1. Multiplication" << endl;	
    cout<<"2. Division" << endl;
    cout<<"3. Addition" << endl;
    cout<<"4. Subtraction" << endl;
    cout<<"5. Exit" << endl;

    cin>> selection;
    cin.ignore();
    
    switch (selection)
	{	
    case 1:
             cout<<"Please input two numbers to be multiplied: ";
             cin>> a >> b;
             cin.ignore();
             cout<<"The product of your two numbers is "<< mult (a,b) <<".\n";
             cin.get();
			 break;
    
	case 2:
             cout<<"Please input two numbers to be divided: ";
             cin>> a >> b;
             cin.ignore();
             cout<<"The product of your two numbers is "<< divi (a,b) <<".\n";
             cin.get();
			 break;

    case 3:
             cout<<"Please input two numbers to be added: ";
             cin>> a >> b;
             cin.ignore();
             cout<<"The product of your two numbers is "<< add (a,b) <<".\n";
             cin.get();
			 break;
    
	case 4:
             cout<<"Please input two numbers to be subtracted: ";
             cin>> a >> b;
             cin.ignore();
             cout<<"The product of your two numbers is "<< subt (a,b) <<".\n";
             cin.get();
			break;

    case 5:
         return 0;
	}
}

//now define what the functions do

int mult (int a,int b)
{
	return a*b;
}

int divi (int a,int b)
{
 return a/b;
}

int add (int a,int b)
{
 return a+b;
}

int subt (int a,int b)
{
 return a-b;
}

Hope that this clarifies it for you, sorry about the long post

Yes, very easily you'll be glad to know. the most convenient
way is a while loop - as shown below. It is very important
to initialise the variable "selection" in circumstances such as these
because as you may or may not know, variables are not
automatically set to zero when you declare them, they have an
undefined value, which is usually the value last stored in the
particular piece of memory - which if that happened to be the
same as the value that the whle loop checks for, then your
program would just exit immediately.

Now i'll briefly explain how this loop works - the while keyword
is a lot like the if keyword - you enter a logical expression into
the parentheses, and if the expression evaluates to true, the
program runs the code inside the braces. if it is false, it skips that
block of code. the condition is checked at the start of each loop,
so that the loop does not exit the moment that the expression
becomes false.

in the code below, the while loop ckecks to see whether the
value stored in selection is 5. if it is not 5, the code inside
the loop is run - allowing the user to make a selection. if they
choose 5, then the switch statement jumps to the label "case 5:"
but the oply thing contained there is a break statement which
exits the switch statement. then the loop itself comes to an
end (there is no code between the end of the switch statement
and the end of the looping block), so the program performs
the while loop check. selection is still 5, so the expression
evaluates to false (it is true for any value except 5, remember?)
and the program skips the code block for the loop. the next line
of code encountered is return 0, so the program exits.

Code:

int main()
{
	int selection = 0;	//Important to initialise this
	int a;				//for the loop to work properly
	int b;

	while (selection != 5)
	{
		cout<<"1. Multiplication" << endl;	
		cout<<"2. Division" << endl;
		cout<<"3. Addition" << endl;
		cout<<"4. Subtraction" << endl;
		cout<<"5. Exit" << endl;

		cin>> selection;
		cin.ignore();
		switch (selection)
		{

			.
			.
			.
			.

		case 5:
			 break;
		}
	}

	return 0;
}