We have already seen conditional expressions in the context of while loops. Conditional expressions can be used with if statements to allow a program to make decisions while it is running. There are numerous applications for if statements. For example, they can be used to detect invalid values and prevent errors:

input_value = 1e99
if input_value > 1e10:
    print("Warning: invalid parameter detected.")
else:
    print("--- Start of iteration ---")

The general syntax for an if statement is the following:

if conditional_expression:
    statements
else:
    statements

The else clause is optional. Python doesn't have a switch statement for choosing between multiple values. Instead, it has a special keyword called elif, which is a contraction of "else if." This can be used to emulate a switch statement. For example, we can use if with elif to choose an algorithm based on user input:

solution_type = "numerical"

if solution_type == "analytical":
    print...