Student Instructions | Week 2 | Topics: Strings, f-strings, input(), if/elif/else

Oregon State University | ENGR 103 | Dr. Cheng Li

Studio Overview

• Theme: Water Quality Reporting System
• Related Reading: Ch 2.3–2.4
• Duration: 90 minutes | All 4 sections run the same activity
• Materials: Laptop with Spyder or Jupyter, this handout

0:00–0:10 — Warm-Up Review

Quick recall: open Spyder, type and run the following without looking at notes:

Recall Exercise

Type and run this code:

x = 3.7
y = '8.2'
print(type(x), type(y))
print(x + float(y))

What will print? Run it and check.

0:10–0:35 — Part 1 — Codedex Warmup (Guided)

Type and run each snippet. Understand what every line does.

Exercise 2A — String Operations

Type and run this code:

species = 'Geobacter sulfurreducens'
print(len(species))           # length
print(species[0])             # first char
print(species[-1])            # last char
print(species[:9])            # first 9 chars
print(species.upper())
print('Geobacter' in species) # membership

# Parsing a sensor data string
reading = 'pH,7.42,DO,8.15,Temp,22.3'
fields = reading.split(',')
print(fields)
print('pH value:', fields[1])

What is fields[3]? What does fields[1::2] give you?

Exercise 2B — f-strings & Formatting

Type and run this code:

station = 'WQ-04'
pH      = 7.326
do      = 8.054
temp_C  = 23.7
temp_F  = temp_C * 9/5 + 32

print(f'Station:     {station}')
print(f'pH:          {pH:.2f}')
print(f'DO:          {do:.3f} mg/L')
print(f'Temperature: {temp_C:.1f}°C / {temp_F:.1f}°F')
print(f'Scientific:  {do:.3e} mg/L')

Add a line that prints BOD = 245.8 mg/L with exactly 1 decimal place.

Exercise 2C — if/elif/else for Water Quality

Type and run this code:

DO = float(input('Enter dissolved oxygen (mg/L): '))

if DO >= 8.0:
    status = 'Excellent'
elif DO >= 6.0:
    status = 'Good'
elif DO >= 4.0:
    status = 'Moderate'
elif DO >= 2.0:
    status = 'Poor'
else:
    status = 'Hypoxic — Critical'

print(f'DO = {DO:.2f} mg/L → Water Quality: {status}')

Test with values: 9.0, 6.5, 3.8, 1.5, 0.0

0:35–1:10 — Part 2 — Practical Lab: Automated Water Quality Report

Work in pairs. Build an interactive water quality checker. The program asks the user for readings and prints a formatted instrument-style report.

Requirements

Your script must:
1. Prompt user for: sample ID (str), pH (float), DO (float), temperature °C (float), BOD (float)
2. Classify overall water quality using ALL parameters:
   - pH: 6.5–8.5 = OK, else FAIL
   - DO: ≥ 6.0 = OK, else FAIL
   - Temp: ≤ 25°C = OK, else FAIL
   - BOD: ≤ 250 mg/L = OK, else FAIL
3. Print a formatted report (see sample output below)
4. Print overall status: PASS (all OK) or FAIL (any parameter fails)

Sample Output

Type and run this code:

==================================== WATER QUALITY REPORT — Sample WQ-07 ==================================== pH: 7.32 [OK] DO: 5.80 [FAIL — below 6.0 mg/L] Temperature: 26.1°C [FAIL — above 25°C] BOD: 180.0 [OK] ------------------------------------ OVERALL STATUS: FAIL ====================================

Match this format as closely as possible.

1:10–1:25 — Part 3 — Extension: Multi-Parameter Alert System

Modify your report to also print a list of which parameters failed and suggest corrective actions.

Extension Logic

Type and run this code:

# After computing ok flags, collect failures:
failures = []
if not pH_ok:
    failures.append(f'pH={pH:.2f} — add buffer')
if not do_ok:
    failures.append(f'DO={DO:.2f} — increase aeration')
if not temp_ok:
    failures.append(f'Temp={temp_C:.1f}°C — cooling needed')
if not bod_ok:
    failures.append(f'BOD={BOD:.0f} — treatment required')

if failures:
    print('\nRequired Actions:')
    for f in failures:
        print(f'  → {f}')

Add this logic to your existing script.

1:25–1:30 — Wrap-Up & TA Check-Off

Demo your Part 2 script to your TA using these test values: ID='WQ-99', pH=5.9, DO=7.2, Temp=24.0, BOD=310. Expected: FAIL (pH + BOD fail).