PricingLoginStart free
C Academy · Lesson

Relational and Logical

Comparisons and &&, ||.

Lesson 2 of 413 steps

Relational and Logical is a free C Academy lesson on CoddyKit. This is lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the C Academy learning path, and your progress syncs across the web and the CoddyKit app. The C Academy course includes 4 lessons in total.

Comparing Values

Relational operators compare two values and produce a truth value: 1 for true and 0 for false.

  • < less than
  • > greater than
  • <= less or equal
  • >= greater or equal
#include <stdio.h>
int main(void) {
    printf("3 < 5 = %d\n", 3 < 5);
    printf("3 > 5 = %d\n", 3 > 5);
    return 0;
}

Equality and Inequality

Use == to test equality and != to test inequality. Do not confuse == with the assignment operator =.

#include <stdio.h>
int main(void) {
    int a = 4, b = 4;
    printf("a == b = %d\n", a == b);
    printf("a != b = %d\n", a != b);
    return 0;
}

Booleans Are Integers

C has no separate boolean type by default. A comparison yields the int values 1 or 0. Any non-zero value counts as true in a condition.

#include <stdio.h>
int main(void) {
    int result = (10 > 2);
    printf("result = %d\n", result);
    return 0;
}

Logical AND

The && operator is true only when both operands are true.

#include <stdio.h>
int main(void) {
    int age = 25;
    if (age > 18 && age < 65)
        printf("Working age\n");
    return 0;
}

Logical OR

The || operator is true when at least one operand is true.

#include <stdio.h>
int main(void) {
    int day = 6;
    if (day == 6 || day == 7)
        printf("Weekend\n");
    return 0;
}

Logical NOT

The ! operator flips a truth value. !0 is 1 and !5 is 0.

#include <stdio.h>
int main(void) {
    int loggedIn = 0;
    if (!loggedIn)
        printf("Please log in\n");
    return 0;
}

Short-Circuit Evaluation

C uses short-circuiting: with && the right side is skipped if the left is false; with || it is skipped if the left is true.

#include <stdio.h>
int main(void) {
    int x = 0;
    if (x != 0 && 10 / x > 1)
        printf("safe\n");
    else
        printf("division skipped\n");
    return 0;
}

Combining Conditions

You can mix relational and logical operators to express rich conditions.

#include <stdio.h>
int main(void) {
    int score = 75;
    if (score >= 50 && score < 80)
        printf("Pass\n");
    return 0;
}

Negating Comparisons

! can wrap a whole comparison. !(a == b) is the same as a != b.

#include <stdio.h>
int main(void) {
    int a = 3, b = 5;
    printf("%d\n", !(a == b));
    return 0;
}

Chaining Is Not Math

Unlike math, 1 < x < 10 does not mean what you expect. It evaluates left to right as comparisons. Use x > 1 && x < 10 instead.

#include <stdio.h>
int main(void) {
    int x = 50;
    if (x > 1 && x < 10)
        printf("in range\n");
    else
        printf("out of range\n");
    return 0;
}

A Decision Example

Combine everything to classify a number.

#include <stdio.h>
int main(void) {
    int n = -4;
    if (n > 0)
        printf("positive\n");
    else if (n < 0)
        printf("negative\n");
    else
        printf("zero\n");
    return 0;
}

Quick Check

Test your understanding of relational and logical operators.

Answer it in the interactive lesson

Recap: Relational and Logical

You learned how to compare and combine conditions.

  • Relational operators yield 1 or 0
  • == != test equality, never confuse == with =
  • && || ! combine truth values
  • Short-circuiting can skip the second operand
  • Chain conditions with explicit &&
Free to start

Learn C with an AI tutor — free

Write and run real code in your browser, get instant help from a 24/7 AI tutor, and pick up where you left off on the web or in the app.

Courses
39
Lessons
144
Start learning freeView the full course

Frequently Asked Questions

Is the “Relational and Logical” lesson free?

Yes — the full text of “Relational and Logical” is free to read here on the web. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the C Academy course, upgrade to CoddyKit PRO. The C Academy course includes 4 lessons in total.

What will I learn in “Relational and Logical”?

Comparisons and &&, ||. You practise C Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start C Academy?

No prior experience is required. C Academy on CoddyKit is structured for beginners through advanced learners, so you can start here or from the beginning and move at your own pace. This is lesson 2 of 4.

How long does the “Relational and Logical” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this C Academy lesson?

Yes. Every C Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Arithmetic Operators
  2. Relational and Logical
  3. Assignment and Increment
  4. Operator Precedence
← Back to C Academy