Calculations: choose the numbers and keep the units

You studied for 150 minutes. How would the program show 2 hours and 30 minutes? Start with the smaller calculations below; keep the units beside your numbers.

Predict four results

An expression produces a value. A value can be a literal such as 7, a variable such as totalHours, or the result of a calculation. Here sessions means the number of study sessions, so totalHours / sessions asks for hours per session.

using System;

int sessions = 2;
int totalHours = 7;

Console.WriteLine(totalHours / sessions);
Console.WriteLine(7m / sessions);
Console.WriteLine(3 + 4 * 2);
Console.WriteLine((3 + 4) * 2);

The type affects the calculation

The suffix m makes 7m a decimal literal. The second division therefore uses decimal arithmetic and produces 3.5. Use decimal when the values and arithmetic need decimal fractions, such as many money calculations. Choosing decimal does not remove the need to think about rounding rules for a real application.

For the positive durations in this lesson, integer division tells us how many complete groups fit. More generally, C# integer division truncates the quotient toward zero. Decide whether you need whole groups or a fractional answer before performing the division. Storing the integer result in a decimal variable afterwards cannot restore the lost fraction.

Multiplication and division have priority over addition and subtraction. Parentheses make the intended grouping explicit. Use them when they help a reader see your intention, especially when translating a written requirement into code. The examples use a dot as the decimal separator; regional display settings can show a comma while representing the same result.

Draw a duration as groups

150 minutes = [60] [60] [30]
                2 whole hours  +  30 minutes left

The division operator / counts the complete 60-minute groups. The remainder operator % gives the part left after those groups. Keep the units beside the calculation: minutes divided by minutes-per-hour gives hours; the remainder is still minutes.

Build the conversion yourself

Write a program that stores 150 total minutes, calculates whole hours and remaining minutes, then prints one labelled sentence. Use variables for the two results. Compare your attempt with this complete solution:

using System;

int totalMinutes = 150;
int wholeHours = totalMinutes / 60;
int remainingMinutes = totalMinutes % 60;

Console.WriteLine($"{wholeHours} hours and {remainingMinutes} minutes");

Now change only totalMinutes to 135. Predict first: the sentence should say 2 hours and 15 minutes. Try 60 and 0 as well; they should produce 1 hour with 0 remaining minutes and 0 hours with 0 remaining minutes. Our output template always prints the word hours; language polishing can come after the calculation is correct.

Explain back: When is integer division useful? Why would changing the type of a variable after dividing fail to recreate a fraction?

References: Microsoft — arithmetic operators, numeric conversions.