C 中的 function 错误返回

Question

I am trying to write a program to compute the GPA of some grades. The idea is to learn how to use functions in C. The following grades correspond to the following numerical values: A = 4, B = 3, C = 2, D = 1 & F= 0.

When inputting the grades in the grades[] array our function should be case insensitive. Here is my code:

#include <stdio.h>
#include <ctype.h>

float compute_GPA(char grades[], int n); 

int main(void)
{
  int n;
  printf("Type length of the array: ");
  scanf("%d", &n);
  char grades[n];

  printf("Type in the (%d) grades you wish to enter: ", n); 

  for(int i = 0; i < n; i++) {
    scanf("%c", &grades[i]);
  }

  printf("The average value is %f\n", compute_GPA(grades, n));

  return 0;
}

float compute_GPA(char grades[], int n)
{
  int sum = 0;
  float average;

  for(int i = 0; i < n; i++) {
    if('a' <= grades[i] && grades[i] <= 'f')
        grades[i] = toupper(grades[i]);

    switch(grades[i]) {
        case 'A': sum += 4; break;
        case 'B': sum += 3; break;
        case 'C': sum += 2; break;
        case 'D': sum += 1; break;
        case 'F': break;
    }   
  }

  average = (float) sum / n;
  return average;
}

After staring at it for a while I can't understand why the arithmetic is wrong. If, say, I let n = 3 and type in AB C for the grades for some reason my answer comes out as 1.3333333 instead of 3.00000 . Likewise it won't let me enter an array of length 1. There is something off and I don't know what it is and it is really bugging me. Any help would be appreciated.

Answer 1

You should use scanf(" %c", &grades[i]); (add space before %c ) instead of scanf("%c", &grades[i]); to have scanf() skip whitespace characters.