Consider the classic staircase problem: given N steps, where you can climb either 1 or 2 steps at a time, calculate the total number of distinct ways to reach the top. This problem maps directly to a Fibonacci-style recurrence relation.

The recursive solution can be implemented in two seemingly different ways, both yielding correct results:

// Version A: Using else if and else
int calculate_paths(int steps) {
    if (steps == 1) {
        return 1;
    } else if (steps == 2) {
        return 2;
    } else {
        return calculate_paths(steps - 1) + calculate_paths(steps - 2);
    }
}

// Version B: Omitting else clauses
int calculate_paths(int steps) {
    if (steps == 1) {
        return 1;
    }
    if (steps == 2) {
        return 2;
    }
    return calculate_paths(steps - 1) + calculate_paths(steps - 2);
}

Version B omits the else if and else keywords, yet functions identically to Version A. This works because the return statement inside each if block immediately halts the function's execution. When steps == 1 evaluates to true, the function returns 1 and exits; the remaining code is never evaluated. The early return guarantees that the logical branches remain mutually exclusive.

However, omitting else is only safe when an early return, break, or similar control flow interrupt is present. Without these, removing else forces the program to evaluate every subsequent if condition, which can lead to cascading logic errors.

For instance, examine a grading logic block that assigns a letter grade based on a numeric score:

// Flawed implementation: omitting else without early returns
char determine_grade(int score) {
    char grade = 'F';
    if (score >= 90) { grade = 'A'; }
    if (score >= 80) { grade = 'B'; }
    if (score >= 70) { grade = 'C'; }
    return grade;
}

In the flawed version, an input of 95 satisfies all three if conditions. Since there is no else to skip the remaining checks, the subsequent conditions score >= 80 and score >= 70 are also evaluated as true, overwriting grade sequentially to 'B' and then 'C'. The function erroneously returns 'C'. Without an immediate exit mechanism like return, omitting else causes all subsequent if blocks to execute sequentially, destroying the intended mutual exclusivity.