C Switch Case Statement

    // Counting letter grades with switch
    #include <stdio.h>
    
    // function main begins program execution
    int main(void)
        {
	int grade; // one grade 
	unsigned int aCount = 0; // number of As
	unsigned int bCount = 0; // number of Bs
	unsigned int cCount = 0; // number of Cs
	unsigned int dCount = 0; // number of Ds
	unsigned int fCount = 0; // number of Fs
	puts("Enter the letter grades.");
	puts("Enter the EOF character to end input.");
    
    // loop until user types end-of-file key sequence
	while ((grade = getchar()) != "EOF") {
    
    // determine which grade was input
		switch (grade) { // switch nested in while
		case 'A': // grade was uppercase A
		case 'a': // or lowercase a
			++aCount; // increment aCount
			break; // necessary to exit switch
		case 'B': // grade was uppercase B
		case 'b': // or lowercase b
			++bCount; // increment bCount
			break; // exit switch
		case 'C': // grade was uppercase C
		case 'c': // or lowercase c
			++cCount; // increment cCount
			break; // exit switch
		case 'D': // grade was uppercase D
		case 'd': // or lowercase d
			++dCount; // increment dCount
			break; // exit switch
		case 'F': // grade was uppercase F
		case 'f': // or lowercase f
			++fCount; // increment fCount
			break; // exit switch
		case '\n': // ignore newlines,
		case '\t': // tabs,
		case ' ': // and spaces in input
			break; // exit switch
		default: // catch all other characters
			printf("%s", "Incorrect letter grade entered.");
			puts(" Enter a new grade.");
			break; // optional; will exit switch anyway
		} // end switch
	} // end while
    // output summary of results
	puts("\nTotals for each letter grade are:");
	printf("A: %u\n", aCount); // display number of A grades
	printf("B: %u\n", bCount); // display number of B grades
	printf("C: %u\n", cCount); // display number of C grades
	printf("D: %u\n", dCount); // display number of D grades
	printf("F: %u\n", fCount); // display number of F grades
} // end function main

    Output:
    Enter the letter grades.
    Enter the EOF character to end input.
    a
    b
    BAf
    C
    E
    Incorrect letter grade entered. Enter a new grade.
    A
    D
    ^Z   end program 
    Totals for each letter grade are:
    A: 3
    B: 3
    C: 1
    D: 1
    F: 1