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Call Cost Calculation in Java

This program demonstrates a simple calculation of call cost based on duration and rate, and then updates a user's balance. It introduces basic Java concepts such as variable declaration, arithmetic operations, and printing output to the console.

Program Code

class CallCostDemo
{
    public static void main(String[] args)
    {
        double bal = 78.5, rate = 0.02;
        int secs = 85;

        System.out.println("Balance B4 Call: " + bal);
        System.out.println("Call Duration: " + secs + " seconds");
        System.out.println("Rate per second: " + rate);

        double cost = secs * rate;
        bal = bal - cost;

        System.out.println("Total cost 4 call: " + cost);
        System.out.println("Balance after call: " + bal);
    }
}

Detailed Explanation

1. class CallCostDemo: This line declares a class named CallCostDemo. In Java, all code resides within classes.
2. public static void main(String[] args): This is the main method, the entry point of any Java application.
   • public: Makes the method accessible from anywhere.
   • static: Allows the main method to be called without creating an object of the class.
   • void: Indicates that the method does not return any value.
   • main: The name of the method.
   • String[] args: An array of strings that can be used to pass command-line arguments to the program.
3. double bal = 78.5, rate = 0.02;:
   • Declares two double type variables: bal (for balance) initialized to 78.5, and rate (for rate per second) initialized to 0.02. double is used for floating-point numbers.
4. int secs = 85;:
   • Declares an int type variable secs (for duration in seconds) initialized to 85. int is used for whole numbers.
5. System.out.println(...): These lines print information to the console.
   • System.out: Is an object that represents the standard output stream.
   • println(): A method that prints the given argument to the console and then moves the cursor to the next line.
   • The + operator concatenates strings and variables.
6. double cost = secs * rate;:
   • Calculates the cost of the call by multiplying secs by rate. The result is stored in a double variable cost.
7. bal = bal - cost;:
   • Updates the bal (balance) by subtracting the cost of the call from it.
8. Final System.out.println statements: These print the calculated cost and the bal after the call.

Program Output

When you compile and run the CallCostDemo program, the output will be:

Balance B4 Call: 78.5
Call Duration: 85 seconds
Rate per second: 0.02
Total cost 4 call: 1.7
Balance after call: 76.8

Flowchart

Here's a flowchart illustrating the program's logic:

graph TD
    A[Start] --> B[Initialize bal = 78.5, rate = 0.02, secs = 85]
    B --> C[Display Initial Balance, Duration, Rate]
    C --> D[Calculate cost = secs * rate]
    D --> E[Update Balance: bal = bal - cost]
    E --> F[Display Total Cost and Final Balance]
    F --> G[End]