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Common Programming Errors in the C Language

VC++ (MFC) Source Codes

SUMMARY

The text below lists some of the most common errors that occur programming in the C language. Any one of these items can cause unpredictable results, such as invalid data.

Using an automatic variable that has not been initialized

Omitting a closing comment delimiter

Using an array index greater than the length of the array (In C, array indexes run from zero to <length>-1.)

Omitting a semicolon or a closing brace

Using an uninitialized pointer

Using a forward slash when a backslash is required (for example, substituting "/n" for "\n.")

Using "=" in a comparison where "==" is desired

Overwriting the null terminator for a string

Prematurely terminating a function declaration with a semicolon (The compiler often flags the "orphan" block of code as a syntax error.)

Specifying the values of variables in a scanf() statement instead of their addresses

Failing to declare the return type for a function

Assuming an expression evaluation order when using an expression with side effects (For example, a[i] = i++; is ambiguous and dangerous.)

Failing to account that a static variable in a function is initialized only once

Omitting a "break" from a case in a switch statement (Execution "falls through" to subsequent cases.)

Using "break" to exit a block of code associated with an if statement (The break statement exits a block of code associated with a for, switch, or while

statement.)

Comparing a "char" variable against EOF (-1). The following idiom results in an infinite loop:

char c;
while ((c = getchar()) != EOF)
{
}

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