Intermediate · C PROGRAMMING

Scope and local variables

What you will learn

Understand which variable a name refers to.

Understand the concept

A variable declared inside a block is visible from its declaration to the end of that block. An inner block may declare another variable with the same name; this hides the outer one within the inner block. Prefer clear names to avoid accidental shadowing.

Read the example

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

Expected output

Inner: 2
Outer: 5

Practise

Rename the inner count to batch_count, then add the outer count to it.

Common mistake

A local variable does not remain accessible after its scope ends. Do not return a pointer to an automatic local variable.

Lesson discussion

#include <stdio.h>

int main(void) {
    int count = 5;
    {
        int count = 2;
        printf("Inner: %d\n", count);
    }
    printf("Outer: %d\n", count);
    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

Inner: 2
Outer: 5

Output will appear here.

Scope and local variables

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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