Lesson 3 · 3 of 20

Arithmetic: div, mod and / · Pascal

Do maths in Pascal: div for whole-number division, mod for the remainder, / for decimal division, and Trunc and Round to get back to integers.

Pascal · Arithmetic: div, mod and / in DMarlon Studio: the example's code and its output in the terminal

`div` divides two integers and keeps the whole part; `mod` gives the remainder. Together they turn 135 minutes into 2 h 15 min and share 17 slices of pizza among 5 friends: 3 each, with 2 left over.

`/` always gives a real number, even when both sides are integers: 17 / 5 is 3.4. That is why the result goes into share, a Double; an Integer variable could not hold it and the compiler would report an error.

As in maths, *, /, div and mod come before + and -: 2 + 3 * 4 gives 14. Brackets change the order: (2 + 3) * 4 gives 20.

To go from a real number to an integer there are two functions: `Trunc` cuts off the decimals (3.7 gives 3) and `Round` rounds (4). Watch out: when a number ends in exactly .5, Round goes to the nearest even number, so Round(2.5) is 2 and Round(3.5) is 4.

42 mod 2 = 0 is the usual way to check whether a number is even: the remainder when you divide it by 2 is zero.

Code · main.pas

program main;var  minutes, slices, friends: Integer;  share: Double;begin  // div divides whole numbers; mod gives the remainder.  minutes := 135;  WriteLn(minutes, ' min = ', minutes div 60, ' h ', minutes mod 60, ' min');  slices := 17;  friends := 5;  WriteLn('Each friend gets ', slices div friends, ' slices');  WriteLn('Slices left over: ', slices mod friends);  // / always gives a real number, even with two integers.  share := slices / friends;  WriteLn('Exact share: ', share:0:2);  // * and / go before + and -; brackets change the order.  WriteLn('2 + 3 * 4 = ', 2 + 3 * 4);  WriteLn('(2 + 3) * 4 = ', (2 + 3) * 4);  // From real to integer: Trunc cuts, Round rounds.  WriteLn('Trunc(3.7) = ', Trunc(3.7), ' | Round(3.7) = ', Round(3.7));  // Round sends .5 to the even number.  WriteLn('Round(2.5) = ', Round(2.5), ' | Round(3.5) = ', Round(3.5));  WriteLn('Even? ', 42 mod 2 = 0);end.

Output · fpc main.pas && ./main

135 min = 2 h 15 min
Each friend gets 3 slices
Slices left over: 2
Exact share: 3.40
2 + 3 * 4 = 14
(2 + 3) * 4 = 20
Trunc(3.7) = 3 | Round(3.7) = 4
Round(2.5) = 2 | Round(3.5) = 4
Even? TRUE

Key points

div is whole-number division and mod the remainder.
/ always returns a real number.
* and / come before + and -; brackets win.
Trunc cuts and Round rounds (halves go to the even number).

Exercise

Turn 7384 seconds into hours, minutes and seconds with div and mod, and print the result as 2 h 3 min 4 s.