Student Grade Calculator in C

Summary: This C program takes a student's percentage score as input and determines their grade using a switch-case statement. The program divides the score by 10 to map it to a single-digit value, making it easier to categorize grades. It also includes error handling for invalid input values.

#include <stdio.h>

int main() {
    int score;
    
    // Taking input from the user
    printf("Enter the student's percentage score: ");
    scanf("%d", &score);
    
    // Using switch-case to determine the grade, including handling invalid input
    switch (score / 10) {
        case 10:
        case 9:
            printf("Grade A\n");
            break;
        case 8:
            printf("Grade B\n");
            break;
        case 7:
            printf("Grade C\n");
            break;
        case 6:
            printf("Grade D\n");
            break;
        case 5:
            printf("Grade E\n");
            break;
        case 4:
        case 3:
        case 2:
        case 1:
        case 0:
            printf("Fail\n");
            break;
        default:
            printf("Invalid Input. Score must be between 0 and 100.\n");
            break;
    }
    
    return 0;
}

Explanation:

Why is the score divided by 10?
The score is divided by 10 (`score / 10`) to simplify the grading logic. Instead of checking multiple individual conditions (e.g., if score >= 90, if score >= 80, etc.), we convert the score into a single-digit integer (0-10). This allows us to map a range of scores to a single case in the switch statement, making the program more concise and readable.

Why use switch-case instead of if-else?
A `switch-case` statement is more efficient and easier to read when dealing with multiple discrete conditions like these grade categories. Instead of writing multiple `if-else` conditions, the switch statement directly maps the computed single-digit value to a corresponding grade.

Why use break statements?
The `break` statement ensures that once a matching case is found, execution stops and exits the switch block. Without `break`, execution would continue into subsequent cases, leading to incorrect results.

Why does the default case exist?
The `default` case acts as a catch-all condition. If the user inputs an invalid score (less than 0 or greater than 100), it prints an error message instead of proceeding with an incorrect grade calculation. This ensures that only valid scores are processed.