while loop not breaking even with break C programming - c

Question

Trying to make a GPA calculator.
Here is my code:
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
int main()
{
float fgpa, grade, n;
char reply;
n = 1;
grade = 1;
printf("--- GPA Calculator ---");
while(fgpa < 1 || fgpa > 4)
{
printf("\n\nEnter your current GPA: ");
scanf("%f", &fgpa);
if(fgpa < 1 || fgpa > 4)
printf("Invalid Input! Please re-enter value.");
}
printf("\nUsing the following table to convert grade to points\n\nA+ = 4.0\nA = 4.0\nB+ = 3.5\nB = 3\nC+ = 2.5\nC = 2.0\nD+ = 1.5\nD = 1\nF = 0\n");
while(grade > 0, n++)
{
printf("\nEnter points for module %.0f, enter \"0\" if there are no more additional modules: ", n);
scanf("%f", &grade);
printf("%f", grade);
fgpa = (fgpa + grade) / n;
}
fgpa = fgpa* n / (n-1);
n--;
printf("\n\nNumber of modules taken: %.0f\nFinal GPA: %.1f", n, fgpa);
return 0;
}
I've tried using if(grade = 0) break; but its still not breaking the loop even when the grade is correctly read 0.
picture of 0 being read correctly but loop still continuing

Answer 1

There are multiple problems in the code:
fgpa is uninitialized so the first test in the loop has undefined behavior.
you should also test the return value of scanf() to detect invalid or missing input.
while (grade > 0, n++) is incorrect too: you should instead always read the next grade and test its value and break from the loop before incrementing n.
Your averaging method seems incorrect too: you do not give the same weight to every module.
It seems more appropriate for your purpose to use for ever loops (for (;;)), unconditionally read input, check for scanf() success and test the input values explicitly before proceeding with the computations.
Here is a modified version:
#include <stdio.h>
// flush the rest of the input line, return EOF at end of file
int flush(void) {
int c;
while ((c = getchar()) != EOF && c != \n')
continue;
return c;
}
int main() {
float fgpa;
float grade;
int n = 1;
char reply;
printf("--- GPA Calculator ---");
for (;;) {
printf("\n\nEnter your current GPA: ");
if (scanf("%f", &fgpa) == 1) {
if (fgpa >= 1 && fgpa <= 4)
break;
}
} else {
if (flush() == EOF) {
fprintf(stderr, "unexpected end of file\n");
return 1;
}
}
printf("Invalid Input! Please re-enter value.\n");
}
printf("\nUsing the following table to convert grade to points\n\n"
"A+ = 4.0\nA = 4.0\nB+ = 3.5\nB = 3\nC+ = 2.5\n"
"C = 2.0\nD+ = 1.5\nD = 1\nF = 0\n");
for (;;) {
printf("\nEnter points for module %d, enter \"0\" if there are no more additional modules: ", n);
if (scanf("%f", &grade) == 1) {
if (grade <= 0)
break;
printf("%f\n", grade);
fgpa = fgpa + grade;
n = n + 1;
} else {
if (flush() == EOF)
break;
printf("Invalid Input! Please re-enter value.\n");
}
}
fgpa = fgpa / n;
printf("\n\nNumber of modules taken: %d\nFinal GPA: %.3f\n", n, fgpa);
return 0;
}