# Soloway's recurring rainfall

Soloway's Recurring Rainfall is commonly used to assess general programming knowledge by requiring basic program structure, input/output, and program exit procedure.

Soloway's recurring rainfall
You are encouraged to solve this task according to the task description, using any language you may know.

The problem:

Write a program that will read in integers and output their average. Stop reading when the value 99999 is input.

For languages that aren't traditionally interactive, the program can read in values as makes sense and stopping once 99999 is encountered. The classic rainfall problem comes from identifying success of Computer Science programs with their students, so the original problem statement is written above -- though it may not strictly apply to a given language in the modern era.

Implementation Details:

• Only Integers are to be accepted as input
• Output should be floating point
• Rainfall can be negative (https://www.geographyrealm.com/what-is-negative-rainfall/)
• For languages where the user is inputting data, the number of data inputs can be "infinite"
• A complete implementation should handle error cases reasonably (asking the user for more input, skipping the bad value when encountered, etc)

The purpose of this problem, as originally proposed in the 1980's through its continued use today, is to just show fundamentals of CS: iteration, branching, program structure, termination, management of data types, input/output (where applicable), etc with things like input validation or management of numerical limits being more "advanced". It isn't meant to literally be a rainfall calculator so implementations should strive to implement the solution clearly and simply.

References:

```with Ada.Text_IO;

procedure RecurringRainfall is
Current_Average : Float := 0.0;
Current_Count : Integer := 0;
Input_Integer : Integer;

-- Recursively attempt to get a new integer
function Get_Next_Input return Integer is
Input_Integer : Integer;
begin
Ada.Text_IO.Put("Enter rainfall int, 99999 to quit: ");
return Input_Integer;
exception
-- We need to call Get_Line to make sure we flush the kb buffer
-- The pragma is to ignore the fact that we are not using the result
pragma Warnings (Off, Clear_String);
-- Recursively call self -- it'll break when valid input is hit
-- We disable the infinite recursion because we're intentionally
-- doing this.  It will "break" when the user inputs valid input
-- or kills the program
pragma Warnings (Off, "infinite recursion");
return Get_Next_Input;
pragma Warnings (On, "infinite recursion");
end Get_Next_Input;

begin
loop
Input_Integer := Get_Next_Input;
exit when Input_Integer = 99999;

Current_Count := Current_Count + 1;
Current_Average := Current_Average + (Float(1) / Float(Current_Count))*Float(Input_Integer) - (Float(1) / Float(Current_Count))*Current_Average;

end loop;
end RecurringRainfall;
```

## ALGOL 68

```BEGIN # read a sequence of integers, terminated by 99999 and outpout their average #
INT end value       = 99999;
INT sum            := 0;
INT count          := 0;
BOOL invalid value := FALSE;
on value error( stand in, ( REF FILE f )BOOL: invalid value := TRUE );
WHILE
INT n := 0;
WHILE
print( ( "Enter rainfall (integer) or ", whole( end value, 0 ), " to quit: " ) );
read( ( n, newline ) );
invalid value
DO
print( ( "Invalid input, please enter an integer", newline ) );
invalid value := FALSE
OD;
n /= end value
DO
sum   +:= n;
count +:= 1;
print( ( "New average: ", fixed( sum / count, -12, 4 ), newline ) )
OD
END```

## BASIC

### Applesoft BASIC

``` 10  LET SUM = 0
20  FOR RAINFALL = 1 TO 1E38
30      INPUT "ENTER RAINFALL (AS AN INTEGER, OR 99999 TO QUIT): ";I
40      IF I = 99999 THEN  END
50      IF I <  >  INT (I) THEN  PRINT "?REENTER, MUST BE AN INTEGER": GOTO 30
60      LET SUM = SUM + I
70      PRINT "  THE NEW AVERAGE RAINFALL IS "SUM / RAINFALL
80  NEXT RAINFALL
```

### QBasic

Works with: QBasic version 1.1
Works with: QuickBasic version 4.5
Works with: FreeBASIC
```n = 0
sum = 0

DO
INPUT "Enter integral rainfall (99999 to quit): ", i
IF i = 99999 THEN
EXIT DO
ELSEIF (i < 0) OR (i <> INT(i)) THEN
PRINT "Must be an integer no less than 0, try again."
ELSE
n = n + 1
sum = sum + i
PRINT "  The current average rainfall is"; sum / n
END IF
LOOP
```
Output:
`Same as FreeBASIC entry.`

### BASIC256

```n = 0
sum = 0

while True
input "Enter integral rainfall (99999 to quit): ", i
if i = 99999 then exit while
if (i < 0) or (i <> int(i)) then
print "Must be an integer no less than 0, try again."
else
n += 1
sum += i
print "  The current average rainfall is "; sum/n
end if
end while```
Output:
`Same as FreeBASIC entry.`

### True BASIC

Works with: QBasic
```LET n = 0
LET sum = 0

DO
PRINT "Enter integral rainfall (99999 to quit): "
INPUT i
IF i = 99999 THEN
EXIT DO
ELSEIF (i < 0) OR (i <> INT(i)) THEN
PRINT "Must be an integer no less than 0, try again."
ELSE
LET n = n + 1
LET sum = sum + i
PRINT "  The current average rainfall is"; sum / n
END IF
LOOP
END
```
Output:
`Same as QBasic entry.`

### Yabasic

```// Rosetta Code problem: https://rosettacode.org/wiki/Soloway%27s_Recurring_Rainfall
// by Jjuanhdez, 09/2022

n = 0
sum = 0

do
input "Enter integral rainfall (99999 to quit): " i
if (i < 0) or (i <> int(i)) then
print "Must be an integer no less than 0, try again."
elsif i = 99999
break
else
n = n + 1
sum = sum + i
print "  The current average rainfall is ", sum/n
end if
loop```
Output:
`Same as FreeBASIC entry.`

## C

```#include <stdio.h>

int main(int argc, char **argv)
{
// Unused variables
(void)argc;
(void)argv;

float currentAverage = 0;
unsigned int currentEntryNumber = 0;

for (;;)
{
int ret, entry;

printf("Enter rainfall int, 99999 to quit: ");
ret = scanf("%d", &entry);

if (ret)
{
if (entry == 99999)
{
printf("User requested quit.\n");
break;
}
else
{
currentEntryNumber++;
currentAverage = currentAverage + (1.0f/currentEntryNumber)*entry - (1.0f/currentEntryNumber)*currentAverage;

printf("New Average: %f\n", currentAverage);
}
}
else
{
printf("Invalid input\n");
while (getchar() != '\n');	// Clear input buffer before asking again
}
}

return 0;
}
```

## C++

```#include <iostream>
#include <limits>

int main()
{
float currentAverage = 0;
unsigned int currentEntryNumber = 0;

for (;;)
{
int entry;

std::cout << "Enter rainfall int, 99999 to quit: ";
std::cin >> entry;

if (!std::cin.fail())
{
if (entry == 99999)
{
std::cout << "User requested quit." << std::endl;
break;
}
else
{
currentEntryNumber++;
currentAverage = currentAverage + (1.0f/currentEntryNumber)*entry - (1.0f/currentEntryNumber)*currentAverage;

std::cout << "New Average: " << currentAverage << std::endl;
}
}
else
{
std::cout << "Invalid input" << std::endl;
std::cin.clear();
std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n');
}
}

return 0;
}
```

## C#

```namespace RosettaCode
{
class CSharpRecurringRainfall
{
{
System.Console.Write("Enter rainfall int, 99999 to quit: ");
string input = System.Console.ReadLine();

if (System.Int32.TryParse(input, out int num))
{
return num;
}
else
{
System.Console.WriteLine("Invalid input");
}
}

static void Main()
{
double currentAverage = 0;
int currentEntryNumber = 0;

for (int lastInput = ReadNextInput(); lastInput != 99999; lastInput = ReadNextInput())
{
currentEntryNumber++;
currentAverage = currentAverage + (1.0/(float)currentEntryNumber)*lastInput - (1.0/(float)currentEntryNumber)*currentAverage;
System.Console.WriteLine("New Average: " + currentAverage);
}
}
}
}
```

## D

```import std.stdio;

void main()
{
float currentAverage = 0;
uint currentEntryNumber = 0;

for (;;)
{
int entry;

write("Enter rainfall int, 99999 to quit: ");

try {
}
catch (Exception e) {
writeln("Invalid input");
continue;
}

if (entry == 99999) {
writeln("User requested quit.");
break;
} else {
currentEntryNumber++;
currentAverage = currentAverage + (1.0/currentEntryNumber)*entry - (1.0/currentEntryNumber)*currentAverage;

writeln("New Average: ", currentAverage);
}
}
}
```

## Fortran

Fortran 90

```function getNextInput() result(Input)
implicit none
integer :: Input
integer :: Reason
Reason = 1

do while (Reason > 0)
print *, "Enter rainfall int, 99999 to quit: "

if (Reason > 0) then
print *, "Invalid input"
end if
enddo

end function getNextInput

program recurringrainfall
implicit none
real        :: currentAverage
integer     :: currentCount
integer     :: lastInput
integer     :: getNextInput

currentAverage = 0
currentCount = 0

do
lastInput = getNextInput()

if (lastInput == 99999) exit

currentCount = currentCount + 1
currentAverage = currentAverage + (1/real(currentCount))*lastInput - (1/real(currentCount))*currentAverage

print *, 'New Average: ', currentAverage
enddo

end program recurringrainfall
```

## FreeBASIC

```Dim As Integer n = 0, sum = 0
Dim As Single i

Do
Input "Enter integral rainfall (99999 to quit): ", i
If i = 99999 Then
Exit Do
Elseif (i < 0) Or (i <> Int(i)) Then
Print "Must be an integer no less than 0, try again."
Else
n += 1
sum += i
Print "  The current average rainfall is"; sum/n
End If
Loop

Sleep
```
Output:
```Enter integral rainfall (99999 to quit): 5.4
Must be an integer no less than 0, try again.
Enter integral rainfall (99999 to quit): -2
Must be an integer no less than 0, try again.
Enter integral rainfall (99999 to quit): 5
The current average rainfall is 5
Enter integral rainfall (99999 to quit): 2
The current average rainfall is 3.5
Enter integral rainfall (99999 to quit): 10
The current average rainfall is 5.6666666666667
Enter integral rainfall (99999 to quit): 99999```

## J

The specification for this task seems inadequate. So, we'll copy some features from other implementations of this task.

Specifically, we'll issue a prompt for every number requested, and reject lines which contain something that is not a number.

Implementation:
```require'general/misc/prompt'

list=. ''
while. do.
y=. (#~ >.=<.)_.".prompt'Enter rainfall int, 99999 to quit: '
if. 99999 e. y do. (+/%#)list return. end.
if. y-:y do. echo 'New average: ',":(+/%#)list=. list,y
else. echo 'invalid input, reenter'
end.
end.
}}
```
Example use:
```   task''
Enter rainfall int, 99999 to quit: 2
New average: 2
Enter rainfall int, 99999 to quit: 3
New average: 2.5
Enter rainfall int, 99999 to quit: 5
New average: 3.33333
Enter rainfall int, 99999 to quit: 7
New average: 4.25
Enter rainfall int, 99999 to quit: 11
New average: 5.6
Enter rainfall int, 99999 to quit: 99999
5.6
```

## Java

```class recurringrainfall
{
private static int GetNextInt()
{
while (true)
{
System.out.print("Enter rainfall int, 99999 to quit: ");
String input = System.console().readLine();

try
{
int n = Integer.parseInt(input);
return n;
}
catch (Exception e)
{
System.out.println("Invalid input");
}
}
}

private static void recurringRainfall() {
float currentAverage = 0;
int currentEntryNumber = 0;

while (true) {
int entry = GetNextInt();

if (entry == 99999)
return;

currentEntryNumber++;
currentAverage = currentAverage + ((float)1/currentEntryNumber)*entry - ((float)1/currentEntryNumber)*currentAverage;

System.out.println("New Average: " + currentAverage);
}
}

public static void main(String args[]) {
recurringRainfall();
}
}
```

## jq

The following program is mainly intended for interactive use. An appropriate invocation would be: jq -nrR -f compute-averages.jq Please note:

• a null response is regarded as an invalid entry;
• if there are no valid entries, the average is not printed;
• leading and trailing spaces in entries are ignored, and a single + or - prefix is allowed;
• an "end-of-file" condition is equivalent to the occurrence of 99999.
```def isinteger: test("^ *[+-]?[0-9]+ *\$");

def soloway:
label \$out
| foreach (inputs, null) as \$x (null;
.invalid = false
| if \$x == null then .break = true
elif (\$x|isinteger) then (\$x|tonumber) as \$n
| if \$n == 99999
then .break = true
else .sum += \$n | .n += 1
end
else .invalid = \$x
end;
if .break then ., break \$out
elif .invalid then .
else empty
end)
| (select(.invalid) | "Invalid entry (\(.invalid)). Please try again."),
(select(.break and .sum) | "Average is: \(.sum / .n)") ;

soloway```

## Julia

Written for simplicity of reading rather than brevity. Changed from the originals to allow negative input, though I note that allowing negative integer input and disallowing floating point seems strange given most "real-life" negative rainfall daily numbers are less than 1 inch.

```"""
Two annotated example outputs
were given: 1) a run with three positive inputs, a zero, and
a negative number before the sentinel; 2) a run in which
the sentinel was the first and only input.
"""
function rainfall_problem(sentinel = 999999, allownegative = true)
total, entries = 0, 0
while true
print("Enter rainfall as \$(allownegative ? "" : "nonnegative ")integer (\$sentinel to exit): ")
n = tryparse(Int, readline())
if n == sentinel
break
elseif n == nothing || !allownegative && n < 0
println("Error: bad input. Try again\n")
else
total += n
entries += 1
println("Average rainfall is currently ", total / entries)
end
end
if entries == 0
println("No entries to calculate!")
end
end

rainfall_problem()
```

## Perl

FWIW

```use strict;
use warnings;

use Scalar::Util qw(looks_like_number);

my (\$periods, \$accumulation, \$rainfall);

sub so_far { printf "Average rainfall %.2f units over %d time periods.\n", (\$accumulation / \$periods) || 0, \$periods }

while () {
while () {
print 'Integer units of rainfall in this time period? (999999 to finalize and exit)>: ';
\$rainfall = <>;
last if looks_like_number(\$rainfall) and \$rainfall and \$rainfall == int \$rainfall;
print "Invalid input, try again.\n";
}
(so_far, exit) if \$rainfall == 999999;
\$periods++;
\$accumulation += \$rainfall;
so_far;
}
```
Output:
```Integer units of rainfall in this time period? (999999 to finalize and exit)>: raindrops
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 2.00
Average rainfall 2.00 units over 1 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: hail
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 10**0
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 1
Average rainfall 1.50 units over 2 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>:
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 999999
Average rainfall 1.50 units over 2 time periods.```

## Phix

```with javascript_semantics
constant inputs = {5.4,"five",5,-2,4,10,99999}
atom n = 0, average = 0
procedure show_average()
printf(1,"  The current average rainfall is %g\n",average)
end procedure

for r in inputs do
printf(1,"Enter integral rainfall, 99999 to quit: %v\n",{r})
if not integer(r) /*or r<0*/ then
--      printf(1,"Must be a non-negative integer, try again.\n")
printf(1,"Must be an integer, try again.\n")
else
if r=99999 then exit end if
n += 1
average += (r-average)/n
show_average()
end if
end for
show_average()
```
Output:
```Enter integral rainfall, 99999 to quit: 5.4
Must be an integer, try again.
Enter integral rainfall, 99999 to quit: "five"
Must be an integer, try again.
Enter integral rainfall, 99999 to quit: 5
The current average rainfall is 5
Enter integral rainfall, 99999 to quit: -2
The current average rainfall is 1.5
Enter integral rainfall, 99999 to quit: 4
The current average rainfall is 2.33333
Enter integral rainfall, 99999 to quit: 10
The current average rainfall is 4.25
Enter integral rainfall, 99999 to quit: 99999
The current average rainfall is 4.25
```

## PureBasic

```Define.i n=0, sum=0
Define.f i

If OpenConsole()
Repeat
Print("Enter integral rainfall (99999 to quit): ")
i=ValF(Input())
If i=99999
Break
ElseIf i<0 Or i<>Int(i)
PrintN("Must be an integer no less than 0, try again.")
Else
n+1
sum+i
PrintN("  The current average rainfall is "+StrF(sum/n,5))
EndIf
ForEver
EndIf
```
Output:
`Same as FreeBASIC entry.`

## Python

```import sys

def get_next_input():
try:
num = int(input("Enter rainfall int, 99999 to quit: "))
except:
print("Invalid input")
return get_next_input()
return num

current_average = 0.0
current_count = 0

while True:
next = get_next_input()

if next == 99999:
sys.exit()
else:
current_count += 1
current_average = current_average + (1.0/current_count)*next - (1.0/current_count)*current_average

print("New average: ", current_average)
```

## Raku

This task seems to be more about following (kind of vague) instructions and anticipating error conditions rather than solving a rather simple problem.

I notice that units are specified for neither measurement; time nor rainfall accumulation. Time is assumed to always increment in units of one, rainfall in some non-negative integer. "Integer" gets a little leeway in this entry. Floating point numbers or Rational numbers that are exactly equal to an Integer are allowed, even if they are technically not integers.

#### After update to spec:

Not going to bother to allow negative rainfall amounts. The "Negative rainfall" cited in the linked article references "total accumulated groundwater" NOT precipitation. Evaporation isn't rainfall. Much like dew or fog is not rainfall.

Further, the linked reference article for Soloway's Recurring Rainfall SPECIFICALLY discusses marking an implementation as incorrect, or at least lacking, if it doesn't ignore and discard negative entries. You can't have it both ways.

```# Write a program that will read in integers and
# output their average. Stop reading when the
# value 99999 is input.

my (\$periods, \$accumulation, \$rainfall) = 0, 0;

loop {
loop {
\$rainfall = prompt 'Integer units of rainfall in this time period? (999999 to finalize and exit)>: ';
last if \$rainfall.chars and \$rainfall.Numeric !~~ Failure and \$rainfall.narrow ~~ Int and \$rainfall ≥ 0;
say 'Invalid input, try again.';
}
last if \$rainfall == 999999;
++\$periods;
\$accumulation += \$rainfall;
say-it;
}

say-it;

sub say-it { printf "Average rainfall %.2f units over %d time periods.\n", (\$accumulation / \$periods) || 0, \$periods }
```
Output:
```# Normal operation
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 0
Average rainfall 0.00 units over 1 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 2
Average rainfall 1.00 units over 2 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 4
Average rainfall 2.00 units over 3 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 6
Average rainfall 3.00 units over 4 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 8
Average rainfall 4.00 units over 5 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 999999
Average rainfall 4.00 units over 5 time periods.

# Invalid entries and valid but not traditional "Integer" entries demonstrated
Integer units of rainfall in this time period? (999999 to finalize and exit)>: a
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 1.1
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>:
Invalid input, try again.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 2.0
Average rainfall 2.00 units over 1 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: .3e1
Average rainfall 2.50 units over 2 time periods.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 999999
Average rainfall 2.50 units over 2 time periods.

# Valid summary with no entries demonstrated.
Integer units of rainfall in this time period? (999999 to finalize and exit)>: 999999
Average rainfall 0.00 units over 0 time periods.```

## Rust

```fn main() {

let mut current_average:f32 = 0.0;
let mut current_entry_number:u32 = 0;

loop
{
let current_entry;

println!("Enter rainfall int, 99999 to quit: ");
let mut input_text = String::new();
let trimmed = input_text.trim();
match trimmed.parse::<u32>() {
Ok(new_entry) => current_entry = new_entry,
Err(..) => { println!("Invalid input"); continue; }
};

if current_entry == 99999
{
println!("User requested quit.");
break;
}
else
{
current_entry_number = current_entry_number + 1;
current_average = current_average + (1.0 / current_entry_number as f32)*(current_entry as f32) - (1.0 / current_entry_number as f32)*current_average;

println!("New Average: {}", current_average);
}
}
}
```

## Wren

Library: Wren-ioutil
```import "./ioutil" for Input

var n = 0
var sum = 0
while (true) {
var i = Input.integer("Enter integral rainfall (99999 to quit): ")
if (i == 99999) break
n = n + 1
sum = sum + i
System.print("  The current average rainfall is %(sum/n)")
}
```
Output:

Sample session:

```Enter integral rainfall (99999 to quit): 5.4
Must be an integer, try again.
Enter integral rainfall (99999 to quit): five
Must be an integer, try again.
Enter integral rainfall (99999 to quit): 5
The current average rainfall is 5
Enter integral rainfall (99999 to quit): -2
The current average rainfall is 1.5
Enter integral rainfall (99999 to quit): 4
The current average rainfall is 2.3333333333333
Enter integral rainfall (99999 to quit): 10
The current average rainfall is 4.25
Enter integral rainfall (99999 to quit): 99999
```

## XPL0

The problem is very simple except for the vague requirements for the user interface and how to deal with unaccepted rainfall amounts.

```real Rain, Sum, Count;
[Sum:= 0.;  Count:= 0.;
loop    [loop   [Text(0, "Enter rainfall amount, or 99999 to quit: ");
Rain:= RlIn(0);
if Rain < 0. then
Text(0, "Must not be negative.^m^j")
else if Floor(Rain) # Rain then
Text(0, "Must be an integer.^m^j")
else quit;
];
if Rain = 99999. then quit;
Sum:= Sum + Rain;
Count:= Count + 1.;
Text(0, "Average rainfall is ");
RlOut(0, Sum/Count);
CrLf(0);
];
]```
Output:
```Enter rainfall amount, or 99999 to quit: 5.4
Must be an integer.
Enter rainfall amount, or 99999 to quit: five
5
Average rainfall is     5.00000
Enter rainfall amount, or 99999 to quit: -2
Must not be negative.
Enter rainfall amount, or 99999 to quit: 4
Average rainfall is     4.50000
Enter rainfall amount, or 99999 to quit:
2.00000001
Must be an integer.
Enter rainfall amount, or 99999 to quit: .3e1
Average rainfall is     4.00000
Enter rainfall amount, or 99999 to quit: 99999
```