C++ Program to Calculate Simple Interest

This article contains some programs in C++, that is used to find/calculate and print simple interest based on the data entered by user at run-time. The data that has to be enter, by user at run-time are:

• principle amount - the money that has to be deposit or borrow
• rate of interest - the interest rate that has to be paid or to receive in return
• time period - for how many years, the money has been deposited, or borrowed

If you're getting confused, about the above data, then forget that, look at the formula of simple interest, given below and then its program. After reading all the things provided here, you'll get to known everything about the program.

Formula to Calculate Simple Interest

The formula to find simple interest is:

SI = (P*R*T)/100

where SI stands for simple interest, P stands for principle amount (deposit or loan amount), R stands for rate of interest, and T stands for time period (in years).

Calculate Simple Interest in C++

The question is, write a program in C++ to find and print simple interest based on the P, R, and T (data) entered by user at run-time. The program given below is the answer to this question:

#include<iostream>

using namespace std;
int main()
{
   float p, r, t, si;
   cout<<"Enter Principle Amount: ";
   cin>>p;
   cout<<"Enter Rate of Interest: ";
   cin>>r;
   cout<<"Enter Time Period: ";
   cin>>t;
   si = (p*r*t)/100;
   cout<<"\nSimple Interest Amount: "<<si;
   cout<<endl;
   return 0;
}

The snapshot given below, taken from the initial output produced by above C++ program of calculating simple interest:

Now enter the data say 246000 as principle amount, 7.5 as rate of interest and 4 as time period, hit ENTER key to calculate and print the simple interest amount like shown in the snapshot given below:

The calculation of simple interest based on P=246000, R=7.5, and T=4 goes in this way:

SI = (P*R*T)/100
   = (246000*7.5*4)/100
   = (246000*30)/100
   = (7380000)/100
   = 73800

That is, you'll get the return of 73800, if you have deposited the amount, otherwise you've to paid 73800, if you've borrowed the loan from individual or bank or from any other sources.

Note - Enter the time period in years only. If you want to go for 6 month, then entered 6/12, that is 0.5 year.

For more interactive and good user-experience program, you can also modify the above program in a way that, user gets options for, whether to enter time period in years or months like shown in the program given below:

#include<iostream>

using namespace std;
int main()
{
   float p, r, t, si;
   char ch;
   cout<<"Enter Principle Amount: ";
   cin>>p;
   cout<<"Enter Rate of Interest: ";
   cin>>r;
   cout<<"Time Period in Year or Month ? (y for year, m for month): ";
   cin>>ch;
   if(ch=='y')
   {
      cout<<"Enter Time Period (in Years): ";
      cin>>t;
      si = (p*r*t)/100;
   }
   else
   {
      cout<<"Enter Time Period (in Months): ";
      cin>>t;
      t = t/12;
      si = (p*r*t)/100;
   }
   cout<<"\nSimple Interest Amount: "<<si;
   cout<<endl;
   return 0;
}

Here is its sample run with 1000 as principle amount, 10 as rate of interest, and m as choice (for months as time period) and finally 4 as total number of months as time period:

Calculate Simple Interest using Function

Let's create the same program, that is, calculating simple interest, but instead of normal process, using a user-defined function named find_si(). This function takes three arguments for p (principle amount), r (rate of interest), and t (time period):

#include<iostream>

using namespace std;

float find_si(float, float, float);
int main()
{
   float p, r, t, si;
   cout<<"Enter Principle Amount: ";
   cin>>p;
   cout<<"Enter Rate of Interest: ";
   cin>>r;
   cout<<"Enter Time Period: ";
   cin>>t;
   si = find_si(p, r, t);
   cout<<"\nSimple Interest Amount: "<<si;
   cout<<endl;
   return 0;
}
float find_si(float a, float b, float c)
{
   float si;
   si = (a*b*c)/100;
   return si;
}

This program produces similar output as produced by previous program. The only difference is, this program is created using a user-defined function.

Calculate Simple Interest using Class

This is the last program created using class. That is, the class CodesCracker is created. Inside the class, I've created a private variable named res, and a public function named find_si(). Now using the class, I've defined the function named find_si() as done in previous program.

Inside the main(), I've created an object of the class CodesCracker. So that, using the object cc_obj, I can access the member function (find_si()) of the class (CodesCracker):

#include<iostream>

using namespace std;

class CodesCracker
{
   private:
      int res;
   public:
      float find_si(float, float, float);
};
float CodesCracker::find_si(float a, float b, float c)
{
   res = (a*b*c)/100;
   return res;
}

int main()
{
   float p, r, t, si;
   CodesCracker cc_obj;

   cout<<"Enter Principle Amount: ";
   cin>>p;
   cout<<"Enter Rate of Interest: ";
   cin>>r;
   cout<<"Enter Time Period: ";
   cin>>t;

   si = cc_obj.find_si(p, r, t);
   cout<<"\nSimple Interest Amount: "<<si;
   cout<<endl;
   return 0;
}

This program also produces similar output as of very first program's output.

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