Finding average for 2 students - c

Question

I am running a program to calculate average for 2 students. I am having trouble running this. For some reason it says it cannot be found. It's my first time using Visual Studio and I am not sure if my code is the problem or the program.
Please check if there's a mistake and let me know.
#include <stdio.h>
int main(void)
{
int firstGrade1;
int sGrade1;
int tGrade1;
int fGrade1;
int TotalGrade1 = (firstGrade1 + sGrade1 + tGrade1 + fGrade1);
int AveGrade1 = (TotalGrade1 / 4);
printf("Please enter Student 1 first grade:\n");
scanf("%d", &firstGrade1);
printf("Please enter Student 1 second grade:\n");
scanf("%d", &sGrade1);
printf("Please enter Student 1 third grade:\n");
scanf("%d", &tGrade1);
printf("Please enter Student 1 fourth grade:\n");
scanf("%d", &fGrade1);
int firstGrade2;
int sGrade2;
int tGrade2;
int fGrade2;
int TotalGrade2 = (firstGrade2 + sGrade2 + tGrade2 + fGrade2);
int AveGrade2 = (TotalGrade2 / 4);
printf("Please enter Student 2 first grade:\n");
scanf("%d", &firstGrade2);
printf("Please enter Student 2 second grade:\n");
scanf("%d", &sGrade2);
printf("Please enter Student 2 third grade:\n");
scanf("%d", &tGrade2);
printf("Please enter Student 2 fourth grade:\n");
scanf("%d", &fGrade2);
printf("1. Student 1 grades:");
printf("%d", firstGrade1, sGrade1, tGrade1, fGrade1);
printf(". Average is ");
printf("%d\n", AveGrade1);
printf("2. Student 2 grades:");
printf("%d", firstGrade2, sGrade2, tGrade2, fGrade2);
printf(". Average is ");
printf("%d", AveGrade2);
system("pause");
return (0);
}

Answer 1

This here
int TotalGrade1 = (firstGrade1 + sGrade1 + tGrade1 + fGrade1);
Doesn't tell it that TotalGrade1 will just always be the value of those 4 variables added up. It assigns to TotalGrade1 the sum of those variables' current values. Since those are uninitialized, that's undefined behavior. Move the calculation of TotalGrade1 and AveGrade1 to after you read in those values, and likewise for TotalGrade2 and AveGrade2, of course.
Also, consider this print:
printf("%d", firstGrade1, sGrade1, tGrade1, fGrade1);
You are printing four int, why is there only one format specifier? The format string should be "%d %d %d %d".
I suggest always paying attention to your compiler's warnings. Usually your compiler should warn you about incorrect printf format strings as well as using uninitialized variables.
On a side note, you have a lot of code duplication. What if you didn't have two students and four grades, but a hundred students with ten grades each? Imagine the amount of code, and the amount of work copy/pasting the code. Instead, try something like this:
int main(void)
{
int Grade[2][4];
int AveGrade[2];
int TotalGrade[2];
for (int i = 0; i < 2; i++) {
for (int j = 0; j < 4; j++) {
printf("Please enter Student %d j. grade:\n", i + 1, j+1);
scanf("%d", &Grade[i][j]);
}
TotalGrade[i] = 0;
for (int j = 0; j < 4; j++)
TotalGrade[i] += Grade[i][j];
AveGrade[i] = (TotalGrade[i] / 4);
}
for (int i = 0; i < 2; i++) {
printf("%d. Student %d grades:", i+1, i+1);
for (int j = 0; j < 4; j++)
printf("%d ", Grade[i][j]);
printf(". Average is ");
printf("%d\n", AveGrade[i]);
}
system("pause");
return (0);
}