The function in my code does not work - c

Question

I tried running the program but it's not running correctly. The problem is at the functions, but I don't know exactly where. I declared the functions first, then I tried calling them in main. However, I'm not sure that's the case. I think the problem is at the function definition ? But I have no clue what else to do. If anyone could look at it and point it out to me that would be great.
#include <stdio.h>
#include <math.h>
float computeMonthlyPayment(float p, float YearRate, float YearTerm);
float computeMonthlyInterest(float p, float YearRate);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
void printTable(float MonthlyPayment, float p, float YearRate,float YearTerm);
int main()
{
float n, p, r, MonthlyPayment, YearRate, YearTerm;
printf("Enter the loan amount: ");
scanf("%f", &p);
if (p <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (p <= 0.0)
{
printf("\nEnter the loan amount: ");
scanf("%f", &p);
}
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
if (YearRate <= 0.0 || YearRate > 30.0)
printf("\nERROR: Invalid rate; must be > 0.0 amd <= 30.0.\n");
while (YearRate <= 0.0 || YearRate > 30.0)
{
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
}
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
if (YearTerm <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (YearTerm <= 0.0)
{
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
}
float computeMonthlyInterest(float p, float YearRate);
float computeMonthlyPayment(float p, float YearRate, float YearTerm);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
return 0;
}
float computeMonthlyPayment(float p, float YearRate, float YearTerm)
{
float r = YearRate/12;
float n = YearTerm*12;
float MonthlyPayment = 0;
MonthlyPayment = (r*p)/1-((1+r)/n);
return MonthlyPayment;
}
float computeMonthlyInterest(float p, float YearRate)
{
float r = 0;
r = ((YearRate)/12)/12;
return r;
}
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n)
{
printf("LOAN INFORMATION\n");
printf("-----------------------\n");
printf("Initial loan amount: %.2f\n", p);
printf("Annual interest rate: %.3f\n", YearRate);
printf("Monthly interest rate: %.3f\n", r);
printf("Term of loan (years): %f\n", YearTerm);
printf("Term of loan (months): %f\n", n);
printf("Monthly payment amount: %.2f\n", MonthlyPayment);
}

Answer 1

Take a look at lines 48..50, in main().
int main()
{
// ...
float computeMonthlyInterest(float p, float YearRate);
float computeMonthlyPayment(float p, float YearRate, float YearTerm);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
// ...
}
Those are the functions' prototypes, not how you actually call them. You're supposed to call them the same way you call printf() or scanf(), by passing them the appropriate parameters. As it stands now, you're just redeclaring the functions in main(), and not actually calling them. Try something like this:
int main()
{
// ...
r = computeMonthlyInterest(p, YearRate); // r should be labeled better.
MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);
// ...
}
This still isn't 100% fixed, though, because n isn't being initialised. While printLoanInfo() says what it's for (this is also how I identified r), you forgot to set it in main(). So..
int main()
{
// ...
r = computeMonthlyInterest(p, YearRate);
n = YearTerm * 12; // You did this in computeMonthlyPayment(), but not here.
MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);
// ...
}
So, with those changes in mind, your main() should probably look like this:
int main()
{
float n, p, r, MonthlyPayment, YearRate, YearTerm;
printf("Enter the loan amount: ");
scanf("%f", &p);
if (p <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (p <= 0.0)
{
printf("\nEnter the loan amount: ");
scanf("%f", &p);
}
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
if (YearRate <= 0.0 || YearRate > 30.0)
printf("\nERROR: Invalid rate; must be > 0.0 amd <= 30.0.\n");
while (YearRate <= 0.0 || YearRate > 30.0)
{
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
}
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
if (YearTerm <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (YearTerm <= 0.0)
{
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
}
// Remove these lines:
// float computeMonthlyInterest(float p, float YearRate);
// float computeMonthlyPayment(float p, float YearRate, float YearTerm);
// void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
// Add these lines:
r = computeMonthlyInterest(p, YearRate);
n = YearTerm * 12;
MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);
return 0;
}

Answer 2

The problem is not the function definitions. It is the fact that, in main(), you have copy and pasted these lines.
float computeMonthlyInterest(float p, float YearRate);
float computeMonthlyPayment(float p, float YearRate, float YearTerm);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
These are function declarations which inform the compiler on HOW to call the functions, but do not actually call them.
If you intend to actually call them, you will need to do something like
variable1 = computeMonthlyInterest(p, YearRate);
variable2 = computeMonthlyPayment(p, YearRate, YearTerm);
printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);
Essentially this removes the type specification from the function arguments and passes actual values. variable1 and variable2 are variables that you will need to define (possibly with more meaningful names) before these statements to hold returned values. Presumably you will also need to write more code in main() to use those variables.

Answer 3

Keeping in mind what the other answers have said concerning calling your functions correctly. The code below should work. I had to rework your computeMonthlyPayment, since it was calculating incorrectly.
#include <stdio.h>
#include <math.h>
float computeMonthlyPayment(float p, float YearRate, float YearTerm);
float computeMonthlyInterest(float p, float YearRate);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
void printTable(float MonthlyPayment, float p, float YearRate,float YearTerm);//why are you defining this if it doesn't exist?
int main()
{
float n=0, p, r=0, MonthlyPayment=0, YearRate, YearTerm;
printf("Enter the loan amount: ");
scanf("%f", &p);
if (p <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (p <= 0.0)
{
printf("\nEnter the loan amount: ");
scanf("%f", &p);
}
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
if (YearRate <= 0.0 || YearRate > 30.0)
printf("\nERROR: Invalid rate; must be > 0.0 amd <= 30.0.\n");
while (YearRate <= 0.0 || YearRate > 30.0)
{
printf("\nEnter annual interest rate: ");
scanf("%f", &YearRate);
}
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
if (YearTerm <= 0.0)
printf("\nERROR: Invalid rate; must be greater than 0\n");
while (YearTerm <= 0.0)
{
printf("\nEnter the term of the loan (in years): ");
scanf("%f", &YearTerm);
}
printLoanInfo(p,MonthlyPayment,YearRate,r,YearTerm,n);
}
float computeMonthlyPayment(float p, float YearRate, float YearTerm)
{
float r = YearRate/(12*100);
float n = YearTerm*12;
return (p*r*pow(1 + r, n)) / (pow(1 + r, n) - 1); // just return the calculation
}
float computeMonthlyInterest(float p, float YearRate)
{
float r = 0;
return (r = ((YearRate)/12)/12);
}
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n)
{
printf("LOAN INFORMATION\n");
printf("-----------------------\n");
printf("Initial loan amount: %.2f\n", p);
printf("Annual interest rate: %.3f\n", YearRate);
printf("Monthly interest rate: %.3f\n", computeMonthlyInterest(p,YearRate)); //call function computeMonthlyInterest
printf("Term of loan (years): %.0f\n", YearTerm);
printf("Term of loan (months): %.0f\n", (YearTerm * 12));//simple calc for number of months
printf("Monthly payment amount: %.2f\n", computeMonthlyPayment(p,YearRate,YearTerm)); // call function computeMonthlyPayment
}