# using formula in C++

In this page, two programs are given. In which real world formulas have been used,

## a simple demonstration to find out simple interest

In this program, we will find simple interest

As we know that we use its formula to find out the simple interest. like

`si = (principle*rate*time/100);`

In this formula, we have input period, rate and time from the user.

Here is the program,

```#include<iostream.h>
#include <conio.h>

void main()
{
clrscr();
int si,principal,rate,time;
cout<<"Enter Principal, rate, time: ";

cout<<"\nPrincipal: ";
cin>>principal;

cout<<"Rate(in %) : ";
cin>>rate;

cout<<"Time(days) : ";
cin>>time;

si = (principal*rate*time/100);

cout<<"Simple interest: "<<si;

getch();
}```
```OUTPUT:-
Enter Principal, rate, time:

Principal : 100
Rate(in %) : 5
Time(days) : 2
Simple interest: 10```

In the program, we have declared three variables. such as,

`int principal, rate, time, si`

Where, the user has been asked for input for variables period, rate and time. suppose these input are

```principal = 100
rate = 5
time = 2```

and variable si store these variable’s result,

`si = (principal*rate*time)/100`

means,

`si = (100*5*2)/100`

And in the last statement, the value of variable si is printed which is 10.

Thus program is executed successfully

Here is another one program,

## Convert Fahrenheit degree to Celsius

in this program we convert fahrenheit degree to celsius

Like the program above, we will use the formula here

`celsius = (farhenheit-32)*5/9;`

Here is the program,

```#include<iostream>
#include<conio.h>
void main()
{
clrscr();
int farhenheit,celsius;

cout<<"Enter Fahrenheit Degree: ";
cin>>farhenheit;

celsius = (farhenheit-32)*5/9; // using formula

cout<<"\nIn Celsius: "<<celsius;

getch();
}```
```OUTPUT:-
Enter Fahrenheit degree: 23
In Celsius: -5```

Explanation:

In the program, we have asked the user to enter the degree farhenheit. Which will be stored in the variable farhenheit, such as,

`farhenheit = 23`

After this we have used the formula to get  celsius degree, so

`celsius = (23-32)*5/9`

And in the last statement, the value of the variable calsius is printed.

Similarly in C++, we can also create many more programs where we can use the formulas.