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LESSON 22 OF 415 · CALCULATIONS WITH NUMBERS

Convert Hours and Minutes into Seconds in Swift

Lesson Read the full explanation

We created two variables to store the number of hours and minutes we worked on a project. We want to convert this amount of time into seconds.

Use these two variables and some arithmetic operations to convert and print to the console the number of seconds the hours and minutes add up to.


Example:

For example, if hours was 1 and minutes was 2, the answer would be 3720.

Why? Because one hour and two minutes add up to 3720 seconds.

Need a hint?


1 hour is made up of 60 minutes. To how many minutes do hours and minutes add up?

hours and minutes add up to hours * 60 + minutes minutes.

Now, how many seconds are there in hours * 60 + minutes minutes?



As 1 minute is made up of 60 seconds, and we have (hours * 60 + minutes) minutes, the answer is: (hours * 60 + minutes) * 60


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    SWIFT · CALCULATIONS WITH NUMBERS

    Convert Hours And Mins Into Seconds in Swift, explained

    Problem overview

    The starter code declares two constants, hours and minutes, which describe how long someone worked on a project. The program must print the same amount of time in seconds.

    For example, 1 hour and 2 minutes is 62 minutes, which is 3720 seconds. With the starter values, 13 hours and 47 minutes, the answer is 49620.

    Approach

    The conversion has two stages, and each one multiplies by 60:

    1. Express the whole duration in minutes. An hour has 60 minutes, so the total is hours * 60 + minutes.
    2. Convert minutes to seconds. A minute has 60 seconds, so multiply the total by 60.

    The second stage applies to the whole minute count, including the part that came from the hours. That is why the first stage has to be finished before the final multiplication, and why the sum needs parentheses.

    Step by step

    1. Turn hours into minutes with hours * 60. For 13 hours this is 780.
    2. Add the minutes. hours * 60 + minutes is 827. Multiplication runs before addition, so no parentheses are needed yet.
    3. Put that sum in parentheses and multiply by 60 to get seconds: (hours * 60 + minutes) * 60. Without the parentheses, only minutes would be multiplied by 60.
    4. Print the result by passing the expression to print.

    The solution in Swift

    let hours = 13
let minutes = 47

print((hours * 60 + minutes) * 60)

    The output is:

    49620

    Swift notes:

    • Integers all the way. Both constants are Int, and so are the literals 60, so the result is an Int and prints without a decimal point.
    • No overflow worry in practice. Int is 64 bits on 64-bit platforms, which hold seconds for far more hours than anyone works. In Swift, an Int that overflows doesn't wrap silently; the program stops with a runtime error.
    • Parentheses are plain grouping. They don't change any value; they only change the order in which Swift computes the pieces.

    Edge cases and common mistakes

    • Multiplying only one part. hours * 60 + minutes * 60 converts the hours to minutes, then treats that count as seconds. For 1 hour and 2 minutes it gives 180 instead of 3720.
    • Forgetting one factor of 60. hours * 60 + minutes gives minutes, not seconds. For 1 and 2 it prints 62.
    • Converting each unit separately. hours * 3600 + minutes * 60 is also correct, because an hour has 3600 seconds. For 13 and 47 it also gives 49620. Both forms are fine, as long as every unit is converted.
    • Zero values. With hours = 0 and minutes = 0, the result is 0. With only minutes, such as 0 and 5, it is 300.

    Testing

    • hours = 1, minutes = 2 prints 3720.
    • hours = 13, minutes = 47 prints 49620.
    • hours = 0, minutes = 5 prints 300.
    • hours = 2, minutes = 0 prints 7200.

    Key takeaways

    • Convert in stages: hours to minutes, then minutes to seconds.
    • Parentheses make sure the final multiplication applies to the whole sum.
    • Check a conversion with a small case you can do by hand, such as 1 hour and 2 minutes.
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