Program that does not return anything - c

Question

I am working on a program in C that can return loan payment.
yearInt is year interest
loanAmt is total amount of loan
monthlyPay is monthly payment
numberPay is number of monthly payment
For some reasons, when I run the program, there is nothing shows up, even I type in a negative number.
Is there anyway to fix it?
#include <stdio.h>
int main(void)
{
float yearInt = -1;
int loanAmt = -1;
float monthlyPay = -1;
int numberPay = -1;
int count = 0;
while (loanAmt<0)
{
printf("Please enter valid loan value: \n");
scanf("%f", &loanAmt);
}
while (yearInt<0)
{
printf("Please enter valid yearly interest value: \n");
scanf("%f", &yearInt)
}
while (monthlyPay<0)
{
printf("Please enter valid monthly payment value: \n");
scanf("%f", &monthlyPay);
}
while (numberPay<0)
{
printf("Please enter valid number of monthly payments: \n");
scanf("%f", &numberPay);
}
if(loanAmt>monthlyPay)
{
while(count<numberPay)
{
loanAmt = loanAmt*(1 + (yearInt/12)) - monthlyPay;
count += count+1;
}
printf("The amount of last payment is: %.2f\n", loanAmt);
else
printf("The amount of last payment is: %.2f\n", loanAmt);
}
return 0;
}

Answer 1

You are using the wrong format specifier to read loanAmount and numberPay. Instead of "%f", use "%d".
scanf("%d", &loanAmt);
and
scanf("%d", &numberPay);
Also, always check the return value of scanf to make sure that it was able to assign data to all the variables.
Change the loop:
while (loanAmt<0)
{
printf("Please enter valid loan value: \n");
scanf("%d", &loanAmt);
}
to
while (loanAmt<0)
{
printf("Please enter valid loan value: \n");
if ( scanf("%d", &loanAmt) != 1 )
{
// Discard the rest of the line.
int c;
while ( (c = fgetc(stdin)) = '\n' && c != EOF );
}
}
It will be still better to put all the checks in a function and call the function from main.
int readInt(char const* prompt)
{
int val = -1;
printf("%s\n", prompt);
while ( scanf("%f", &val) != 1 || val < 0)
{
// Discard rest of the line.
int c;
while ( (c = fgetc(stdin)) = '\n' && c != EOF );
// If EOF is reached, we have a problem.
if ( c == EOF )
{
exit(0);
}
printf("%s\n", prompt);
}
return val;
}
and then, use:
loanAmount = readInt("Please enter valid loan value: ");
Add a similar function to read floats and call it for reading the variables that are of type float.

Answer 2

scanf("%f", &loanAmt); // loanAmt is int
...
scanf("%f", &numberPay); //numberPay is int
In both wrong argument is passed to %f , therefore , causes UB . Use %d specifier .
And in this one } is missing -
if(loanAmt>monthlyPay)
{
while(count<numberPay)
{
loanAmt = loanAmt*(1 + (yearInt/12)) - monthlyPay;
count += count+1;
}
printf("The amount of last payment is: %.2f\n", loanAmt); //use %d
// ADD '}' here
else // ADD '{' here
printf("The amount of last payment is: %.2f\n", loanAmt); //use %d
}
Put a } before else {.