無止盡的Coding地獄

The simple interest on a loan is calculated by the formula
interest = principal * rate * days / 365;
The preceding formula assumes that rate is the annual interest rate, and therefore includes thedivision by 365 (days). Develop a program that will input principal, rate and days for several loans, and will calculate and display the simple interest for each loan, using the preceding formula. Here is a sample input/output dialog:

********************************

#include <stdio.h>
#include <stdlib.h>

int main ()
{
    float principal;
    float rate;
    int days;
    float interest;
    do
    {
          printf("Enter loan principal (-1 to end): ");
          scanf("%f",&principal);
          printf("Enter interest rate: ");
          scanf("%f",&rate);
          printf("Enter term of the loan in days: ");
          scanf("%d",&days);
          
          interest = ( principal * rate * days ) / 365;
          printf("The interest charge is $%f",interest);
    }while( principal == -1 );
    system("PAUSE");
    return 0;
}