Selection

if mark >= 70:
    grade = "A"
elif mark >= 60:          # Java: else if
    grade = "B"
elif mark >= 50:
    grade = "C"
else:
    grade = "F"

print(grade)

if (mark >= 70) {
    grade = "A";
} else if (mark >= 60) {
    grade = "B";
} else if (mark >= 50) {
    grade = "C";
} else {
    grade = "F";
}

System.out.println(grade);

# WRONG — separate ifs for exclusive cases
if mark >= 50: grade = "C"
if mark >= 60: grade = "B"
if mark >= 70: grade = "A"
# a mark of 75 sets C, then B, then A — it only works by accident

# WRONG — right structure, wrong order
if mark >= 50:   grade = "C"      # 75 matches here first
elif mark >= 70: grade = "A"      # never reached

// WRONG — separate ifs for exclusive cases
if (mark >= 50) { grade = "C"; }
if (mark >= 60) { grade = "B"; }
if (mark >= 70) { grade = "A"; }
// a mark of 75 sets C, then B, then A — it only works by accident

// WRONG — right structure, wrong order
if (mark >= 50)      { grade = "C"; }   // 75 matches here first
else if (mark >= 70) { grade = "A"; }   // never reached

# Both must hold
if age >= 16 and has_permission:
    print("Allowed")

# Either will do
if day == "Saturday" or day == "Sunday":
    print("Weekend")

# Reversing a condition
if not is_member:
    print("Please join first")

# A common mistake
if day == "Saturday" or "Sunday":     # always true — "Sunday" alone is not a test
    ...

// Both must hold
if (age >= 16 && hasPermission) {
    System.out.println("Allowed");
}

// Either will do
if (day.equals("Saturday") || day.equals("Sunday")) {
    System.out.println("Weekend");
}

// Reversing a condition
if (!isMember) {
    System.out.println("Please join first");
}

// A common mistake
if (day == "Saturday") { }   // compares REFERENCES, not the text — use .equals