declaring variables without any data type in c

by

What you see here is the “Implicit Int Rule” at work. Simply put the rule says:

“A variable declared without an explicit type name is assumed to be of type int.”

Note that this rule was revoked in the c99 Standard[Ref 1].However, depending on your compiler and its settings, the first example might compile with a warning, or will fail to compile(with strict compilation settings)

If you compile your first example with strict settings adhering to c99 Standard the compiler will tell you the root cause.

check here.

cc1: warnings being treated as errors
prog.c:1: error: data definition has no type or storage class
prog.c:1: error: type defaults to ‘int’ in declaration of ‘a’
prog.c:3: error: return type defaults to ‘int’
prog.c: In function ‘main’:
prog.c:4: error: implicit declaration of function ‘printf’
prog.c:4: error: incompatible implicit declaration of built-in function ‘printf’

EDIT:

why does the first example work but second does not?

Note the emphasis on the words “variable declared” in the rule.

In first example, since the statement is at the global scope it is treated as an Implicit declaration, and the Implicit Int Rule gets applied to it.

In Second example, the statement acts as an Assignment and not a Declaration. Since there is no declaration the Implicit int rule does not apply here. In the absence of any type the compiler cannot determine what is the type of a and hence reports the error.

[Ref 1]

C99 Standard: Foreword
Para 5:

This edition replaces the previous edition, ISO/IEC 9899:1990, as amended and corrected
by ISO/IEC 9899/COR1:1994, ISO/IEC 9899/COR2:1995, and ISO/IEC 9899/AMD1:1995.
Major changes from the previous edition include:
…..
…..
— remove implicit int
…..
…..

More Related Contents:

  1. How I can correct my c code?
  2. Variable redeclaration in c in loop and outside loop?
  3. How to resolve a variable for char length? [closed]
  4. BigInteger in C?
  5. Why is the asterisk before the variable name, rather than after the type?
  6. How does an uninitiliazed variable get a garbage value?
  7. Why are global variables always initialized to ‘0’, but not local variables? [duplicate]
  8. Concatenating Variable Names in C?
  9. Where are constant variables stored in C?
  10. Get warning when a variable is shadowed
  11. In C, what is the correct syntax for declaring pointers?
  12. How to place a variable at a given absolute address in memory (with GCC)
  13. Printing all global variables/local variables?
  14. shared global variables in C
  15. C Programming: Forward variable argument list
  16. ISO C90 forbids mixed declarations and code in C
  17. Why does fgetc() return int instead of char?
  18. How are variable names stored in memory in C?
  19. Programmatic way to get variable name in C?
  20. C multiple single line declarations
  21. C variable declarations after function heading in definition [duplicate]
  22. Varying string variable in an if condition
  23. How are static variables with the same name in different functions identified by the System?
  24. Difference between static global variable and non-static global variable in C [duplicate]
  25. Why do we separately cast to “float” in an integer division?
  26. Uninitialized variable in C [duplicate]
  27. lvalue required as increment operand
  28. Regex to pull out C function prototype declarations?
  29. Error: initializer element is not computable at load time
  30. How to convert 32-bit float to 8-bit signed char? (4:1 packing of int32 to int8 __m256i)

Leave a Comment