Grade Calculator

Program to calculate grade based on marks

BeginnerTopic: Conditional Programs

JavaScript Grade Calculator Program

This program helps you to learn the fundamental structure and syntax of JavaScript programming.

// Grade system:
// 90-100: A
// 80-89: B
// 70-79: C
// 60-69: D
// Below 60: F

function calculateGrade(marks) {
    if (marks >= 90 && marks <= 100) {
        return 'A';
    } else if (marks >= 80 && marks < 90) {
        return 'B';
    } else if (marks >= 70 && marks < 80) {
        return 'C';
    } else if (marks >= 60 && marks < 70) {
        return 'D';
    } else if (marks >= 0 && marks < 60) {
        return 'F';
    } else {
        return 'Invalid marks';
    }
}

// Test cases
console.log("95 marks:", calculateGrade(95));
console.log("85 marks:", calculateGrade(85));
console.log("75 marks:", calculateGrade(75));
console.log("65 marks:", calculateGrade(65));
console.log("45 marks:", calculateGrade(45));
console.log("105 marks:", calculateGrade(105));

// Method 2: Using switch with ranges
function calculateGrade2(marks) {
    switch(true) {
        case marks >= 90 && marks <= 100:
            return 'A';
        case marks >= 80 && marks < 90:
            return 'B';
        case marks >= 70 && marks < 80:
            return 'C';
        case marks >= 60 && marks < 70:
            return 'D';
        case marks >= 0 && marks < 60:
            return 'F';
        default:
            return 'Invalid marks';
    }
}

console.log("\nUsing switch:");
console.log("92 marks:", calculateGrade2(92));
console.log("78 marks:", calculateGrade2(78));

Output

95 marks: A
85 marks: B
75 marks: C
65 marks: D
45 marks: F
105 marks: Invalid marks

Using switch:
92 marks: A
78 marks: C

Understanding Grade Calculator

This program demonstrates range-based conditional logic.

Grade System

Common grading scale:

A

: 90-100 (Excellent)

B

: 80-89 (Good)

C

: 70-79 (Average)

D

: 60-69 (Below Average)

F

: 0-59 (Fail)

Method 1: If-Else Chain

Checking ranges with AND operator:

if (marks >= 90 && marks <= 100) {
} else if (marks >= 80 && marks < 90) {

    return 'B';
}

// ... and so on

    return 'A';

Range Checking

•marks >= 90 && marks <= 100: Inclusive range

•marks >= 80 && marks < 90: Lower inclusive, upper exclusive

Method 2: Switch with Ranges

Using switch(true) pattern:

switch(true) {
    case marks >= 90 && marks <= 100:
    case marks >= 80 && marks < 90:

        return 'B';
    // ...
}

        return 'A';

Switch(true) Pattern

•Evaluates each case as boolean

•First matching case executes

•Useful for range checks

Input Validation

Always validate input:

if (marks < 0 || marks > 100) {
}

    return 'Invalid marks';

Real-world Applications

•Student grading systems

•Performance evaluation

•Score categorization

•Rating systems

When to Use:

If-else

: Most common, readable

Switch

: Multiple ranges, organized

Let us now understand every line and the components of the above program.

Note: To write and run JavaScript programs, you need to set up the local environment on your computer. Refer to the complete article Setting up JavaScript Development Environment. If you do not want to set up the local environment on your computer, you can also use online IDE to write and run your JavaScript programs.

Practical Learning Notes for Grade Calculator

This JavaScript program is part of the "Conditional Programs" topic and is designed to help you build real problem-solving confidence, not just memorize syntax. Start by understanding the goal of the program in plain language, then trace the logic line by line with a custom input of your own. Once you can predict the output before running the code, your understanding becomes much stronger.

A reliable practice pattern is to run the original version first, then modify only one condition or variable at a time. Observe how that single change affects control flow and output. This deliberate style helps you understand loops, conditions, and data movement much faster than copying full solutions repeatedly.

For interview preparation, explain this solution in three layers: the high-level approach, the step-by-step execution, and the time-space tradeoff. If you can teach these three layers clearly, you are ready to solve close variations of this problem under time pressure.

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