Question

Description:

The purpose of this assignment is to write code that calculates the amount of interest accrued on a credit card on its expenses. You will create a C program that prompts the user for the total amount of purchases on the credit card, an annual percentage rate (APR), and the number of days the money is borrowed. The program will calculate the amount of the compound interest for the purchases, then print the original amount of purchases, the amount of the interest, and the total amount needed to be paid back.

Preparation:

• Read the man pages for fgets(), sscanf(), and printf() noting how format strings are used in each function. Pay careful attention to how floating point values are printed with printf() and how to create a reference to a variable when using sscanf() (use the & before the variable that is to contain the input).
• Read the man page for pow().

• Your program will prompt the user to enter a value for the amount of expenses on the credit card. Retrieve the user input using fgets()/sscanf() and save the input value in a variable. The value should be read as type double. The user may or may not enter cents as part of the input. In other words, expect the user to enter values such as 500, 500.00 and 500.10. The program will then prompt the user to enter the Annual Percentage Rate (APR) for the credit card. This value should also be read as type double and saved in a second variable. Next, your program will prompt the user to enter the number of days money is borrowed. This value should be read as type int. After the values have been entered, your program will calculate the amount of the interest and save the result in a fourth variable. The program will then add the interest amount to the expense amount and save this result in a fifth variable. Finally, it will print all five variables (expense amount, APR, number of days, amount of interest and total amount to be paid back) to the screen in an informative format. Ensure that the floating point output always displays exactly two decimal places. Also, values of a magnitude less than 1 should display a leading 0 (ex. 0.75).

• 
  For interest calculation, we will use the compound interest method, in which, we consider not only the interest on the actual borrowed amount, but also the interest of interest that has already accrued. We will use the following simple formula to compute compound interest:
  
           P' = P(1 + r/n)^(nt)
  
           where:
           P is the original principal sum
           P' is the new principal sum
           r is the annual interest rate
           n is the compounding frequency (we assume it to be 12, like most US banks)
           t is the overall length of time the interest is applied (expressed in years).
  
  The total compound interest generated is the final value minus the initial principal:
  
           I = P' - P
  
  In order to compute the power function, you need to include math.h library and call the pow() function within it. See the man page of pow() to find more information about it. Also note that, the number of days money is borrowed needs to be converted to number of years. If you simply try days/365 to express it in terms of years, the result of the division is likely going to be incorrect.
  
  Your program should check to ensure that negative values are not input. If an improper value is entered, an error message should be printed and the program will exit (do not re-prompt the user for a correct value).
  
  For input, you must use the fgets()/sscanf() combination of Standard I/O functions. Do not use the scanf() or fscanf() functions. Although using scanf() for retrieving numerical data is convenient, it is problematic when used in conjunction with character string input (as you may discover if you use it in later labs). Therefore, it is best to get into the habit of avoiding scanf() completely, and using the fgets()/sscanf() combination exclusively.
  
  Although you will learn more about this in later lectures and labs, this is what you should typically do to read a number using the fgets()/sscanf() combination:

  // in main() or some function
  char inBuf[20]; // A buffer to hold the input from the keyboard
  int someInt = 0; // A variable to hold the number from the keyboard
  
  fgets(inBuf, 20, stdin); // Read the input from the keyboard and store it in inBuf
  sscanf(inBuf, "%d", &someInt); // Extract the numerical value from inBuf and store it in someInt

  Note from the sscanf() manpage that when reading a floating point value, if the data type of the variable that will receive the value is of type double, you must use "%lf" (long float) instead of "%f" (float) for your format string.

Answer 1

#include <stdio.h>
#include <math.h>

int main()
{
char inBuf[15]; // A buffer to hold the input from the keyboard
double expense, arp, ci, ci_y, ci_d, intrest, rate;
int n_days, years, days;

printf("Enter value for the amount of expenses on the credit card : ");
fgets(inBuf, 15, stdin); // Read the input from the keyboard and store it in inBuf
sscanf(inBuf, "%lf", &expense); // Extract the double value from inBuf and store it in expense

printf("Enter the Annual Percentage Rate (APR) for the credit card : ");
fgets(inBuf, 15, stdin);
sscanf(inBuf, "%lf", &arp);

printf("Enter the number of days money is borrowed : ");
fgets(inBuf, 15, stdin);
sscanf(inBuf, "%d", &n_days);

if( expense < 0 || arp < 0 || n_days < 0){ // if any entered value are negative then exit
printf("\nError...Improper value is entered");
return 0;
}

years = n_days / 365; // calculating number of years
days = n_days % 365; // calculating number of days

rate = arp/100;

ci_y = expense * pow((1 + rate / 12), 12*years); // CI for years
ci_d = expense * pow((1 + rate / 365), days); // CI for days

ci = ci_y + ci_d; // Adding both CIs

intrest = ci - (2 * expense);

printf("\nExpense Amount : %.2lf\n",expense);
printf("Annual Percentage Rate (APR) : %.2lf\n",arp);
printf("Number of days : %d\n",n_days);
printf("Amount of interest : %.2lf\n",intrest);
printf("Total amount to paid back : %.2lf\n",expense + intrest);

return 0;
}
Output :