C Operators

Calculate and compare values with operators whose types, order, and side effects you can explain.

Arithmetic operators transform numeric values

Multiplication, division, and remainder happen before addition and subtraction. When both operands of / or % are integers, the result is an integer: 17 % 5 is 2, and 7 / 2 is 3. If a fraction matters, make at least one operand floating-point, as C Data Types explains.

#include <stdio.h>

int main(void) {
  int pages_per_chapter = 8;
  int chapters = 3;
  int total_pages = pages_per_chapter * chapters;
  int whole_groups = total_pages / 5;
  int spare_pages = total_pages % 5;

  printf("Total pages: %d\n", total_pages);
  printf("Groups of five: %d, spare: %d\n", whole_groups, spare_pages);
  return 0;
}

Edit the program, predict its output, then run it.

Assignment stores; increment updates by one

= is not a math claim. It evaluates the right side, then stores the result in the left-side object. Compound forms such as += and -= are shorthand for “read, calculate, store.” Prefix ++n updates then yields the new value; postfix n++ yields the old value then updates. In beginner code, n = n + 1; is often the clearest form.

#include <stdio.h>

int main(void) {
  int checked_in = 12;

  checked_in = checked_in + 1;
  printf("%d learners have checked in.\n", checked_in);
  return 0;
}

Edit the program, predict its output, then run it.

Comparison and logical operators produce conditions

Equality needs two characters: == compares, = assigns. Relational operators are < <= > >=. Logical && requires both sides, || accepts either, and ! inverts. C treats zero as false and nonzero as true. Using these operators inside if is the job of C If Else; this lesson is the catalog of the operators themselves.

#include <stdio.h>

int main(void) {
  int score = 82;
  int passing = 70;

  if (score >= passing && score != 0) {
    puts("Ready to report.");
  } else {
    puts("Check the score.");
  }
  return 0;
}

Edit the program, predict its output, then run it.

Bitwise operators & | ^ ~ << >> exist in C. This course uses them only when a later systems topic needs them; do not treat them as a substitute for && and ||.

Make grouping visible

C evaluates ! before comparisons, comparisons before &&, and && before ||. Arithmetic * / % bind tighter than + -. You do not need to rely on that table for a complicated rule: parentheses or a named intermediate value make the intended grouping obvious.

Compile mixed expressions with conversion warnings

Independent lab: one named calculation

Write a program that computes a total with *, a group count with /, and a remainder with %, then prints whether the remainder is zero using ==. Predict each line before you run it.

Lesson review

• Arithmetic, assignment, increment, comparison, and logical operators are separate jobs.
• Integer / and % stay in the integer domain.
• == compares; = stores.
• Parentheses or named intermediates beat a memorized precedence table.