how can i impliment a #define statement into my code? - c

Question

First off, how can I implement a #define in this code? I'm fairly lost when it comes to defining and calling of that #define. Also, if there are any ways to make this code look better it would be greatly appreciated! I'm new to coding so any help would be awsome. This is technically homework but I met all the requirements for the assignment so now this is simply exploratory.
#include <stdio.h>
#include <math.h>
int main() {
int studentID;
int count= 0;
char course1[10]={};//issue with storing user input, used an array
char course2[10]={};
float coursecost1;
float coursecost2;
float credithour = 120.25;
float healthID=35.00;
float totalcost;
// Asks for student ID
printf("Enter the Students Id: \n");
scanf("%d",&studentID);
// Enter CRN/Credit hrs for first course
printf("Enter crn/credit hours for the first course: \n");
scanf("%s", &course1);
// Enter CRN/Credit hrs for Second Course
printf("Enter crn/credit hours for the second course: \n");
scanf("%s", &course2);
// Closing statement
printf("\nThank you!\nPRESS ANY KEY TO CONTINUE...\n\n");
// Calculates Cost of Class
int i = course1[5]-'0'; // Bad version of type casting from char to int.
int k = course2[5]-'0'; // Bad version of type casting from char to int.
coursecost1 = i*credithour;
coursecost2 = k*credithour;
totalcost= healthID+coursecost1+coursecost2;
// Printout
printf("\t\tVALENCE COMMUNITY COLLEGE\n\t\tORLANDO FL 10101\n\t\t");
do{
count++;
printf("*");
}while(count<26);
printf("\n\t\tFee Invoice Prepared for Student V%d\n",studentID);
printf("\t\t1 Credit Hour = %.2f\n",credithour);
printf("\t\tCRN\t CREDIT HOURS\n");
printf("\t\t%c%c%c%c\t %c\t\t $
%.2f\n",course1[0],course1[1],course1[2],course1[3],course1[5],coursecost1);
printf("\t\t%c%c%c%c\t %c\t\t $
%.2f\n",course2[0],course2[1],course2[2],course2[3],course2[5],coursecost2);
printf("\t\t\t Health & id fees $ %.2f\n",healthID);
printf("\t\t");
count=0;
do{ //could define a function to clean up code
count++;
printf("-");
}while (count < 39);
printf("\n\t\t\t Total Payments $ %.2f",totalcost);
return 0;

Answer 1

"define" is basically creating a shortcut for stuff you write often in your code, or stuff you want to change often in order to test your code.
An example:
#define fail printf("You did something wrong")
int main (void)
{
int number;
printf("Insert a number between 1 and 3");
scanf("%d", &number);
if (number>3||number<1)
{
fail;
return -1
}
else
{
printf("Insert a number between 4 and 6");
scanf("%d", &number);
if (number<4||number>6)
{
fail;
return -1;
}
else return 0;
}
}
When this program is read by the compiler, every "fail" gets substituted by "printf("you did something wrong").
This is the main use of define, and if you are beginning now, that's what I'd consider important.
About your code, when you do scanf for strings, don't use "&", or use the "gets" function. I could try to explain why to you, but I'm not the best person for this job. My tip is, keep studying and when you start seeing pointers, you'll understand better why this happens.
Also, when you use arrays without a starting value, you don't need to do the "={ }" thing, just call them without "=".
Now, as you asked, this is how I'd write your code, with the corrections done:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main() {
int studentID, intcount = 0; // Count is a function, better not mix things up, that's why I called it "intcount"
char course1[10], course2[10];
float coursecost1, coursecost2, totalcost;
float credithour = 120.25;
float healthID=35.00;
// Asks for student ID
printf("Enter the Students Id: \n");
scanf("%d",&studentID);
// Enter CRN/Credit hrs for first course
printf("Enter crn/credit hours for the first course: \n");
scanf("%s", course1);
// Enter CRN/Credit hrs for Second Course
printf("Enter crn/credit hours for the second course: \n");
scanf("%s", course2);
// Closing statement
// printf("\nThank you!\nPRESS ANY KEY TO CONTINUE...\n\n");
/* Decided not to delete this one, so you can
compare this printf with the new one and the system pause */
printf("\nThank you!\n");
system("pause");
// Calculates Cost of Class
// I'm not sure what you were trying to do in these lines, so I won't touch them
int i = course1[5]-'0';
int k = course2[5]-'0';
coursecost1 = i*credithour;
coursecost2 = k*credithour;
totalcost= healthID+coursecost1+coursecost2;
// Printout
printf("\t\tVALENCE COMMUNITY COLLEGE\n\t\tORLANDO FL 10101\n\t\t");
do
{
intcount++;
printf("*");
}
while(intcount<26);
printf("\n\t\tFee Invoice Prepared for Student V%d\n",studentID);
printf("\t\t1 Credit Hour = %.2f\n",credithour);
printf("\t\tCRN\t CREDIT HOURS\n");
printf("\t\t%c%c%c%c\t %c\t\t $%.2f\n",course1[0],course1[1],course1[2],course1[3],course1[5],coursecost1);
printf("\t\t%c%c%c%c\t %c\t\t $%.2f\n",course2[0],course2[1],course2[2],course2[3],course2[5],coursecost2);
printf("\t\t\t Health & id fees $ %.2f\n",healthID);
printf("\t\t");
intcount=0;
do
{ //could define a function to clean up code
intcount++;
printf("-");
}
while (intcount < 39);
printf("\n\t\t\t Total Payments $ %.2f",totalcost);
}
Basically just try to avoid placing too much information on the same line, even split single printfs into multiple ones if neccessary.
Hope I could be of some use!