Default data type of parameter in C?

Question

I am new to C and have a question. I think I made a mistake, but the compiler is not giving a warning and the program runs fine. I believe there is an error in line 4: ``` #include <stdio.h> void void_int(int x); void void_int(x) { // <-- no type definition for parameter x printf( "void_int: %d
", x); } int main(int argc, char **argv) { printf("Hello world
"); // declare a function pointer void (*by_ref_void_int)(int); // assign pointer to a function by_ref_void_int = &void_int; // run referenced function by_ref_void_int(2); return 0; } ``` I do not define a type for the first argument to the function definition `void void_int(x) {`, however, gcc is not giving me any errors. The program runs just fine. I compile with: `gcc -Wall -o fp fp.c`. Would anybody help me trying to understand? Is there a default type for function arguments and is it possibly int? Thanks and best wishes -S ``` $ gcc -v Using built-in specs. COLLECT_GCC=/usr/bin/gcc-4.7.real COLLECT_LTO_WRAPPER=/usr/lib/gcc/x8…

Accepted Answer

to keep the compatibility with arcaic versions of the `C` language, if a declaration specifies no type, the default type is assumed to be `int`.

If you simply specify a version of the language, the compiler will surely help you spotting this

```
gcc -std=c99 a.c
a.c: In function ‘void_int’:
a.c:4:6: warning: type of ‘x’ defaults to ‘int’ [enabled by default]
 void void_int(x) { // <-- no type definition for parameter x
      ^
```

try to specify a version of the language, it's always a good habit that will help you.

Default data type of parameter in C?

Solution

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