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Opening and closing braces for if, for, or while statements should always be used , even if the statement's body contains only a single statement.

If an if, while, or for statement is used in a macro, the macro definition should not conclude with a semicolon. (See recommendation PRE11-C. Do not conclude macro definitions with a semicolon.)

Braces improve the uniformity and readability of code. More importantlyimportant, when inserting an additional statement into a body containing only a single statement, it is easy to forget to add braces because the indentation gives strong (but misleading) guidance to the structure.

Braces also help ensure that macros with multiple statements are properly expanded. Such a macro should be wrapped in a do-while loop. (See recommendation PRE10-C. Wrap multi-statement macros in a do-while loop.) However, when the do-while loop is not present, braces can still ensure that the macro expands as intended.

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int login;

if (invalid_login())
  login = 0;
else
  login = 1;

A developer might add a debugging statement to determine when the login is valid , but forget to add opening and closing braces.

int login;

if (invalid_login())
  login = 0;
else
  printf("Login is valid\n");  /* debugging line added here */
  login = 1;                   /* this line always gets executed, regardless of a valid login! */

Due to the Because of the indentation of the code, it is difficult to tell that the code will not function as intended by the programmer, potentially leading to a security breach.

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int login;

if (invalid_login()) {
  login = 0;
} else {
  login = 1;
}

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This noncompliant code example has an if statement nested in another if statement without braces around the if and else bodies.

int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
else
  privileges = ADMINISTRATOR;

...

int privileges;

if (invalid_login())
  if (allow_guests())
    privileges = GUEST;
  else
    privileges = ADMINISTRATOR;

...

int privileges;

if (invalid_login()) {
  if (allow_guests()) {
    privileges = GUEST;
  } 
} else {
  privileges = ADMINISTRATOR;
}

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Related Guidelines

ISO/IEC 9899:19992011 Section 6.8.4, "Selection statements"

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