23.2: Generating Random Number

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To request a random number, a real variable must be declared and then passed to the following call to the built-in random_number() routine. For example:

call random_number(x)

The random number between 0.0 and 1.0 such that 0.0 \(\leq\) random number \(<\) 1.0.

In order to obtain a larger number, it can be multiplied by an appropriate scale. For example, to simulating the roll of a dice, a random integer number between 1 and 6 would be required. The following code would obtain the random number and then scale it and convert to integer as required.

call random_number(x)
die = int(x*6.0) + 1

Since the 0.0 is a possible value and 1.0 is not ( 0.0 \(\leq\) random number \(<\) 1.0) 1 is added to ensure that 0 cannot be assigned to the variable die. Further, since .999 is the largest possible value (since 1.0 is not), and .999 * 6 will generate 6 (5.9 truncated to 5 with 1 added).