Predefined function in c++ - c++

Question

This is my first time on this web site. I have been having a problem but I haven`t been able to figure it out. I have been trying to implement a predefined function into my code but I am not sure how to do so. In my Task I was given an open brief asking me simply to design a password protected calculator. I designed the calculator and handed it in to my teacher. He then asked me to add a predefined function. Now I am not sure how to do this or even how I would start. Could any one give me some example of a predefined function similar to my code.
#include <iostream>
using namespace std;
int main()
{
char op;
float num1, num2;
int correct_password = 1998;
int password = 0;
int counter = 0;
int attempt = 0;
while (attempt <= 3) {
cout << "Enter your password: ";
cin >> password;
attempt = attempt + 1;
if (password != correct_password) {
cout << "Incorrect password combination. Please try again." << "\n" << endl;
} else {
break;
}
}
if (attempt >= 3) {
return 0;
}
cout << "Access granted." << endl;
//Asks you to enter an operator to use in your calculation
cout << "Enter operator either + or - or * or /: ";
cin >> op;
//Asks you to enter 2 numbers
cout << "Enter two operands: ";
cin >> num1 >> num2;
//Searches for which operator you have selected and Either *-+/ the number depending on choice
switch (op) {
case '+':
cout << num1 + num2;
break;
case '-':
cout << num1 - num2;
break;
case '*':
cout << num1 * num2;
break;
case '/':
cout << num1 / num2;
break;
//If entered operator is incorrect closes down the program
default:
cout << "Error! operator is not correct";
break;
}
return 0;
}
Sorry for the trouble. I am not quite sure if I am going about asking this the right way. so I will apologies before hand if I am not specific enough or if I am doing ti wrong :).

Answer 1

(edit:: added some explanation)
I can't know what exactly your teacher wanted, but it might be something like this:
void foo(float a, float b){
return a+4*b;
}
Allowing your calculator to use a function like that would work in the following way:
... //Your previous code here
switch(op){
... // Your other switches here
case 'f':
cout<<foo(num1,num2)<<endl;
break;
}
... //Your following code here
The 'f' here stands for the command "EXECUTE PREDEFINED FUNCTION" instead of '+' for "ADD" or '-' for "SUBTRACT".
That way you could have a predefined function and execute that on your numbers.
In this case we would see the entred number num1 be added to four times the entered number num2
I hope it helped :)

Answer 2

these function are in library #include<math.h> You need to use this header file in order to use those function in your code .
It includes predefined functions such as
sqrt(number);
This function is used to find square root of the argument passed to this function.
pow(number);
This is used to find the power of the given number.
trunc(number);
This function truncates the decimal value from floating point value and returns integer value