Introduction to Conditional Statements

When the Path Changes

A conditional statement lets a program choose a path based on an input or situation. The important idea is not just writing an if statement; it is designing the program so that each possible input reaches the correct outcome. Overtime pay, invalid user input, and grade assignment all require the program to make a decision and then execute only the appropriate branch.

Overtime at the Threshold

The overtime problem has a clear decision point at 40 hours. When the number of hours is 40 or less, the regular-pay path is used. When the number is greater than 40, only the hours above 40 receive the 1.5x multiplier. The first 40 hours remain on the regular-pay path.

hours = 45 rate = 20 if hours > 40: regular_hours = 40 overtime_hours = hours - 40 pay = regular_hours * rate + overtime_hours * rate * 1.5 else: pay = hours * rate print(pay)

Protecting Input Conversion

User input may not be numeric when the program expects a number. A try block can contain the conversion and processing steps, while an except block provides a graceful response when the conversion cannot handle the supplied input. This keeps the program from simply failing at the point where the unexpected input appears.

try:
    hours = float(input("Enter hours worked: "))
    print("Hours accepted:", hours)
except:
    print("Please enter a numeric value.")

Validating Before Processing

Range validation adds another decision after input has been converted. The program first determines whether the value is within the accepted range. Valid input continues to the conditional processing, while invalid input receives an invalid-input response. This prevents values outside the intended range from being treated as normal cases.

For a score represented between 0.0 and 1.0, values such as 1.5 and -0.1 should be treated as out of range. Boundary values deserve special attention because they test whether comparisons include or exclude the exact threshold.

Chaining Grade Decisions

A multi-branch conditional checks several possible ranges in sequence. The illustrative grading logic below first rejects scores outside 0.0 through 1.0. It then checks the highest threshold first and continues through lower thresholds until one matches. The final else branch handles the remaining valid scores.

try:
    score = float(input("Enter a score from 0.0 to 1.0: "))

    if score < 0.0 or score > 1.0:
        print("Invalid score")
    elif score >= 0.9:
        print("A")
    elif score >= 0.8:
        print("B")
    elif score >= 0.7:
        print("C")
    elif score >= 0.6:
        print("D")
    else:
        print("F")
except:
    print("Please enter a numeric score.")

For a score of 0.85, the output is B. For a score of 1.5, the output is Invalid score. For text that cannot be converted to a number, the except branch prints Please enter a numeric score.

Testing Every Boundary

Conditional logic should be tested with normal inputs, boundary values, edge cases, and intentionally bad input. For overtime, test fewer than 40 hours, exactly 40 hours, and more than 40 hours. For exception handling, test numeric input, text, negative values, and very large values. For grading, test the threshold values 0.9, 0.8, 0.7, and 0.6, values between them, and out-of-range values such as 1.5 and -0.1.

• Applying the 1.5x multiplier to all hours

  The multiplier applies only to hours above 40, not to the first 40 hours.

  Fix: Separate regular hours from overtime hours before applying the multiplier.

• Testing only ordinary values

  A conditional can appear correct while mishandling the threshold itself.

  Fix: Test values below the threshold, exactly at the threshold, and above it.

• Treating non-numeric input as a valid number

  Text supplied where a number is expected may prevent the intended processing path.

  Fix: Place the conversion in try and provide a graceful response in except.

• Skipping range validation

  An input can be numeric but still outside the accepted range.

  Fix: Validate the range before running the grade thresholds.

• Debugging the result without checking the branch

  The error may be that a different conditional path was selected.

  Fix: Print the input and log which branch was taken immediately after each condition.

Practice the Paths

Conditional Logic Checklist

1. A conditional statement routes an input to a particular processing path.
2. For overtime pay, the 40-hour threshold separates regular processing from overtime processing, and only hours above 40 receive the 1.5x multiplier.
3. A try and except structure lets a program respond gracefully when input cannot be converted to a number.
4. Range validation should happen before further conditional processing when only a specific input range is valid.
5. Boundary values, edge cases, and intentionally bad input reveal whether every branch works as intended.