Initializing Switch Case - c

Question

I'm building a program using a grade report and I'm having trouble calculating my GPA using a switch case. I'm unsure why it isn't assigning the correct values. I would also like if there is a way to ask for the number of classes taken and then get the loop to perform that said number of times.
Here is the code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Grades
{
char Name[20];
int Hrs;
int ID;
char ClassName[20];
char Grade;
char ClassID[6];
};
int main ()
{
struct Grades Transcript[6];
int classCnt = 0;
int vHrs=0, vGPA=0, totalHours=0, totalPoints = 0;
char vGrade;
char vName[20], vCID[6], vClassName[20];
printf("Enter Students Name: ");
fgets(vName, 20, stdin);
do
{ printf("\nEnter Class ID: ");
fgets(vCID, 6, stdin);
fflush(stdin);
strcpy_s(Transcript[classCnt].ClassID, vCID);
printf("Enter Class Name: ");
fgets(vClassName, 20, stdin);
strcpy_s(Transcript[classCnt].ClassName, vClassName);
printf("Enter Class Hours: ");
fflush(stdin);
scanf("%d", &vHrs);
Transcript[classCnt].Hrs = vHrs;
printf("Enter Class Grade: ");
fflush(stdin);
scanf("%c", &vGrade);
Transcript[classCnt].Grade = vGrade;
classCnt++;
fflush(stdin);
totalHours+=vHrs;
switch (vGrade) {
case 'A':
case 'a': 4*vHrs;
break;
case 'B':
case 'b': 3*vHrs;
break;
case 'C':
case 'c': 2*vHrs;
break;
case 'D':
case 'd': 1*vHrs;
break;
case 'F':
case 'f': 0;
break;
default: printf("Invalid Grade");}
totalPoints += vGrade;
vGPA = (totalPoints/totalHours);
}while(classCnt<=5);
printf("********************************** Grade Report: *************************************");
printf("\n%d\n", totalHours);
printf("%d\n", vGPA);
system("Pause");
return 0;

Answer 1

The expression statement:
4*vHrs;
is certainly valid in C but it doesn't actually do anything (a).
Perhaps you may want to assign it to something, such as with:
addPoints = 4 * vHrs;
(declaring addPoints beforehand, of course) and then use that to affect totalPoints later:
totalPoints += addPoints;
In terms of asking for a class count, you can use scanf("%d",...) to get an integer from the user and then just use that integer in a loop:
#include <stdio.h>
int main (void) {
int num, count;
printf ("Enter countdown value: ");
scanf ("%d", &count);
for (num = count; num > 0; num--)
printf ("%d ", num);
puts ("BLAST OFF");
return 0;
}
A sample run being:
Enter countdown value: 10
10 9 8 7 6 5 4 3 2 1 BLAST OFF
(a) Even a statement like 42; is valid, though useless. The reason this is allowed is because you can have side effects in expressions. The classic case, though not many learners immediately see this, is the venerable i++;.
This is an expression which gives you the current value of i (which you throw away unless you're using it somehow), then increments i as a side effect.

Answer 2

case 'A':
case 'a': 4*vHrs;
break;
case 'B':
case 'b': 3*vHrs;
break;
case 'C':
case 'c': 2*vHrs;
break;
case 'D':
case 'd': 1*vHrs;
break;
case 'F':
case 'f': 0;
None of these lines have any effect on the program you've written. You might want to assign 3*vHrs, 4*vHrs etc to a variable and then do the calculations below. You probably meant vHrs *= 3 or vHrs *=4 or something like that?