C++ Handbook

`default` — C Keyword

`default` — C Keyword

The default keyword in C: fallback branch in a switch statement.

How to use this reference page

Use reference pages to confirm names, categories, nearby facilities, and the constraints that matter before writing or reviewing code.

  • Scan the top of the page first to identify the primary types, functions, or algorithm families involved.
  • Use the nearby-page links when your question is really about a companion header, related algorithm family, or broader subsystem.
  • Validate tricky behavior with a small compileable example before relying on memory for details like invalidation, ordering, allocation, or lifetime rules.

default (C)

Marks the fallback branch in a switch statement, executed when no case label matches.

Syntax

switch (expr) {
    case N: ...
    default: statements
}

Example

#include <stdio.h>

int main(void) {
    int code = 99;

    switch (code) {
        case 0:  printf("OK\n");      break;
        case 1:  printf("Error\n");   break;
        default: printf("Unknown\n"); break;  /* executed */
    }
    return 0;
}

Notes

Example in practice

int main() {
    // Pick one facility from this reference page.
    // Write the smallest program that exercises its main precondition,
    // complexity rule, or lifetime constraint before scaling up.
    return 0;
}