Operators & Conditions — ToolScope Notes

Free PDF of this lesson — save it, print it, revise offline. The video is the same lesson on the Code Scope YouTube channel.

Introduction

Data alone does nothing — apps must calculate and decide. Operators are Dart's calculation symbols (+, *, ~/, % and friends), and conditions are how a program chooses a path: if marks are high, print "Grade A"; otherwise, print something else. This lesson covers the arithmetic set, the true/false operators, and the three decision tools — if / else, switch and the one-line ternary. (Roman Urdu: Operator hisaab karta hai, condition faisla — dono mil kar program ko dimagh dete hain.)

Key points

Arithmetic operators: + add, - subtract, * multiply, / divide (always gives a double: 17 / 5 = 3.4), ~/ divide and keep only the whole part (17 ~/ 5 = 3), % remainder (17 % 5 = 2).(Roman Urdu: ~/ poora hissa deta hai, % baqi bacha hua — dono roz kaam aate hain.)
Comparison operators answer with true or false: == equal, != not equal, > greater, < smaller, >= and <=. One = puts a value in a box; two == ask whether two values match. Mixing them up is the classic bug.
Logical operators combine answers: && (AND — both must be true), || (OR — any one true is enough), ! (NOT — flips true to false).
if / else if / else runs the first branch whose condition is true, and skips all the rest. Conditions go in ( ), the branch's work goes in { }.
switch is cleaner than a long if chain when one value has many fixed choices (day numbers, menu options). Each case ends with break;, and default catches everything else.
The ternary condition ? valueIfTrue : valueIfFalse is a one-line if/else that gives a value — perfect for small choices like age >= 18 ? 'Adult' : 'Minor'.

Code examples

Example 1 — Arithmetic: the full set on two numbers

void main() {
  int a = 17;
  int b = 5;

  print(a + b); // 22
  print(a - b); // 12
  print(a * b); // 85
  print(a / b); // 3.4 — hamesha double
  print(a ~/ b); // 3 — sirf poora hissa
  print(a % b); // 2 — baqi (remainder)
}

What it does: Six prints show the six operators on the same two numbers. Comments on the right show the expected answer — always check your program against answers you already know, like a calculator you trust.

What you will see: six lines — 22, 12, 85, 3.4, 3, 2. The pair ~/ and % together split 17 into "3 groups of 5, remainder 2" — exactly how you would split 17 rotis among 5 people.

Example 2 — The grade program (if / else if / else)

void main() {
  int marks = 82;

  if (marks >= 90) {
    print('Grade A');
  } else if (marks >= 75) {
    print('Grade B');
  } else if (marks >= 50) {
    print('Pass');
  } else {
    print('Fail');
  }
}

What it does: Dart checks the conditions from the top. 82 is not ≥ 90, so the first branch is skipped; 82 is ≥ 75, so "Grade B" prints and every branch below is ignored — even though 82 is also ≥ 50. Order is logic: always write the biggest condition first.

What you will see: one line — Grade B. Change marks to 95 and only Grade A prints; change to 30 and only Fail prints. One run, one branch — never two.

Example 3 — switch for fixed choices + the ternary shortcut

void main() {
  int day = 3;
  String dayName;

  switch (day) {
    case 1:
      dayName = 'Monday';
      break;
    case 3:
      dayName = 'Wednesday';
      break;
    default:
      dayName = 'Some other day';
  }
  print(dayName);

  int age = 20;
  String result = age >= 18 ? 'Adult' : 'Minor';
  print(result);
}

What it does: The switch matches day against fixed cases — 3 lands on the case 3 branch and stores 'Wednesday'. The ternary then makes a two-way choice in a single line and stores the value it picked in result.

What you will see: two lines — Wednesday and Adult. Remove any break; and Dart warns you — in Dart's classic switch, break is what stops the program from falling into the next case.

Quick recap

/ gives a double, ~/ gives the whole part, % gives the remainder.
= assigns; == compares. Comparisons answer true or false.
&& both true, || any true, ! flips the answer.
if / else if / else — first true branch wins; write conditions biggest first.
switch for many fixed choices on one value; ternary for a one-line two-way choice.

Common mistakes

Using = inside a condition — if (marks = 50) tries to assign and Dart errors. A question always uses ==. Read your condition aloud: "is marks equal to 50?" — if it sounds like a question, it needs ==.
Wrong branch order in grade-style chains — if you check >= 50 before >= 90, a student with 95 gets "Pass" instead of "Grade A", because the first true branch wins. Biggest and strictest conditions go on top.
Forgetting break in switch — without break;, Dart complains and the logic can fall through into the next case. Every case ends with break; — make it a habit while typing the case itself.

Practice

Write a program that stores a temperature and prints "Garam", "Normal" or "Thanda" using if / else if / else (above 35, 20–35, below 20).
Take a number in a variable and print whether it is even or odd — hint: number % 2 == 0 means even. Use a ternary to print the answer in one line.