How to find largest among three numbers in ALGOL?

To find the largest among three numbers in ALGOL, you can compare the numbers using the if-else statements. Below is how you can achieve this.

• Define and initialize your three variables with the numbers to be compared. Make sure to use the correct ALGOL syntax for defining the variables, e.g. REAL a := 12.0; REAL b := 15.0; REAL c := 10.0;. Here, we are initializing a with 12, b with 15 and c with 10.

• Set up a if condition to check if the first number is greater than the other two numbers. If it is, then you can conclude that it is the largest. The syntax would look something like this: if a > b AND a > c THEN outString("a is the largest").

• If the first number is not greater than the other two, then control will move to the else part of the condition. In the else part, set up another condition to compare the second and the third number. The syntax would look like this: else if b > c THEN outString("b is the largest"). If b is not the largest, then it is implied that c is the largest. Thus you can print a message to indicate that c is the largest.

• The above steps, when put together, yield the following code:

BEGIN
    REAL a := 12.0;
    REAL b := 15.0;
    REAL c := 10.0;

    IF a > b AND a > c 
    THEN 
        outString("a is the largest") 
    ELSE 
        IF b > c 
        THEN 
            outString("b is the largest") 
        ELSE
            outString("c is the largest")
    END IF
END IF
END

Don't forget, outString is a hypothetical function; please replace it with your actual output method.

This is a basic way to find the largest of three numbers in ALGOL. If you have more than three numbers, you can update the code to accommodate those. Also, there are other ways and algorithms to find the largest number from a given set. Depending on the specific situation and problem constraints, other methods might be more efficient.