Beginner · C PROGRAMMING

Conditions and logical operators

What you will learn

Choose a branch using if, else and logical expressions.

Understand the concept

An if statement executes its body when its expression is nonzero. Use comparison operators such as >= and <= to produce a true or false result. The && operator requires both conditions to be true; || accepts either condition.

Read the example

The complete program appears below. Read it first, predict the output, then run it.

Expected output

Check temperature

Practise

Test the values -1, 0, 40 and 41. Explain why the boundary values matter.

Common mistake

Use == to compare equality. A single = assigns a value and can silently change a condition.

Lesson discussion

#include <stdio.h>

int main(void) {
    int temperature = 42;
    if (temperature >= 0 && temperature <= 40) {
        puts("Normal range");
    } else {
        puts("Check temperature");
    }
    return 0;
}

PRACTICE LAB

Read. Edit. Run.

C source · .c

Experiment with the program below. Your code and input are sent to the selected compiler only when you run it.

Compiler

C source

Tab indents · Shift+Tab unindents · Esc then Tab leaves the editor · Ctrl/Cmd+Enter runs · Ctrl/Cmd+S saves a draft

Changes save automatically to your account.

Standard input

Input / output example

Example input

No input required.

Expected output for the original program

Check temperature

Output will appear here.

Conditions and logical operators

What you will learn

Understand the concept

Read the example

Expected output

Practise

Common mistake

Lesson discussion

Read. Edit. Run.

Input / output example

Debugging Lab

Interactive Memory Visualizer

Stack frames

Memory and pointers

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