Lesson 4 · 4 of 20

Formatting output · Pascal

Shape numbers in Pascal: WriteLn with :width:decimals and the Format function from SysUtils to line up the columns of a café receipt.

Pascal · Formatting output in DMarlon Studio: the example's code and its output in the terminal

With no instructions, WriteLn prints a real number in scientific notation: 3.4560000000000000E+000. Adding `:0:2` after the value prints it with two decimals, rounded: 3.46. The first number is the minimum width and the second the number of decimals.

When the width is larger than the value, it is padded with spaces on the left: price:8:2 takes up 8 characters, and 42:6 and 'tea':6 take up 6, aligned to the right. It is the quickest way to make columns.

For more control there is `Format`, from the `SysUtils` unit (which is why the program starts with uses SysUtils;). It takes a pattern and, in square brackets, the values that fill it: %s is a string, %d an integer and %.2f a real number with two decimals.

The width goes between the % and the letter: %4d takes up 4 characters aligned right and %-10s takes up 10 aligned left, thanks to the minus sign. That is how the receipt columns line up. To print an actual %, write %%.

Code · main.pas

program main;uses  SysUtils;var  price: Double;begin  price := 3.456;  // With no format, a real number comes out in scientific notation.  WriteLn(price);  // :0:2 means as wide as needed, with two decimals.  WriteLn(price:0:2);  // :8:2 fills up to 8 characters, aligned to the right.  WriteLn('[', price:8:2, ']');  WriteLn('[', 42:6, ']', '[', 'tea':6, ']');  // Format, from SysUtils, builds a string from a pattern.  WriteLn(Format('%-10s%4s%9s', ['Item', 'Qty', 'Euros']));  WriteLn(Format('%-10s%4d%9.2f', ['Coffee', 2, 2.40]));  WriteLn(Format('%-10s%4d%9.2f', ['Croissant', 3, 4.65]));  WriteLn(Format('%-10s%4d%9.2f', ['Juice', 1, 2.10]));  WriteLn(Format('%-14s%9.2f', ['Total', 9.15]));  WriteLn(Format('VAT included: %d%%', [10]));end.

Output · fpc main.pas && ./main

 3.4560000000000000E+000
3.46
[    3.46]
[    42][   tea]
Item       Qty    Euros
Coffee       2     2.40
Croissant    3     4.65
Juice        1     2.10
Total              9.15
VAT included: 10%

Key points

value:width:decimals formats numbers in WriteLn.
:0:2 prints two decimals with no extra spaces.
Format('pattern', [values]) lives in SysUtils.
%d, %s and %.2f; a - aligns to the left.

Exercise

Add a Unit column to the receipt with the price of each item (1.20, 1.55 and 2.10) and one more line with two pieces of toast at 1.80; fix the total.