INFO: Common Programming Errors in the C Language

• Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
• Microsoft C/C++ for MS-DOS, version 7.0
• Microsoft Visual C++ for Windows, versions 1.0, 1.5
• Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.0, 4.0, 5.0

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)
           {
           }
  

Keywords          : CLngIss kbfasttip
Version           : MS-DOS:5.1,6.0,6.00a,6.00ax,7.0; WINDOWS:1.0,1.5; WINDOWS  NT:1.0,2.0,4.0,5.0
Platform          : MS-DOS NT WINDOWS
Issue type        : kbinfo