C program to calculate electricity bill

Write a C program to input electricity unit charge and calculate the total electricity bill according to the given condition:
For first 50 units Rs. 0.50/unit
For next 100 units Rs. 0.75/unit
For next 100 units Rs. 1.20/unit
For unit above 250 Rs. 1.50/unit
An additional surcharge of 20% is added to the bill.

Logic to calculate net electricity bill

Step by step descriptive logic to compute electricity bill.

1. Input unit consumed by customer in some variable say unit.
2. If unit consumed less or equal to 50 units. Then amt = unit * 0.50.
3. If unit consumed more than 50 units but less than 100 units. Then add the first 50 units amount i.e. 25 to final amount and compute the rest 50 units amount. Which is given by amt = 25 + (unit-50) * 0.75. I have used units-50, since I already calculated first 50 units which is 25.
4. Similarly check rest of the conditions and calculate total amount.
5. After calculating total amount. Calculate the surcharge amount i.e. sur_charge = total_amt * 0.20. Add surcharge amount to net amount. Which is given by net_amt = total_amt + sur_charge.

/**
 * C program to calculate total electricity bill
 */

#include <stdio.h>

int main()
{
    int unit;
    float amt, total_amt, sur_charge;

    /* Input unit consumed from user */
    printf("Enter total units consumed: ");
    scanf("%d", &unit);


    /* Calculate electricity bill according to given conditions */
    if(unit <= 50)
    {
        amt = unit * 0.50;
    }
    else if(unit <= 150)
    {
        amt = 25 + ((unit-50) * 0.75);
    }
    else if(unit <= 250)
    {
        amt = 100 + ((unit-150) * 1.20);
    }
    else
    {
        amt = 220 + ((unit-250) * 1.50);
    }

    /*
     * Calculate total electricity bill
     * after adding surcharge
     */
    sur_charge = amt * 0.20;
    total_amt  = amt + sur_charge;

    printf("Electricity Bill = Rs. %.2f", total_amt);

    return 0;
}

/*
Output :

Enter total units consumed: 150
Electricity Bill = Rs. 120.00
*/