A magic number 127 in my C book [duplicate]

Question

Possible Duplicate:
What limits the number of nested loops in c?

Hello.

When I read my C book, it says

Nesting for-Loop in C can continue even further up to 127 levels!

How does 127 come from?

My book doesn't mention about this. Just like a magic number to me.

[update]

int main()
{
    int number, n, triangularNumber, counter;

    triangularNumber = 0;

    for (counter = 1; counter <= 5; ++counter){
        printf("What triangular number do you want? \n");

        // using a routine called scanf
        scanf("%i", &number);


        triangularNumber = 0;

        for (n =1 ; n <= number; ++n)

            triangularNumber += n;

        printf("Triangular number %i is %i\n", number, triangularNumber);
    }
    return 0;
}

Answer 1

This number comes from the ISO C standard, ISO/IEC 9899:1999:

5.2.4.1 Translation limits

The implementation shall be able to translate and execute at least one program that contains at least one instance of every one of the following limits:

• 127 nesting levels of blocks
• 63 nesting levels of conditional inclusion
• 12 pointer, array, and function declarators (in any combinations) modifying an arithmetic, structure, union, or incomplete type in a declaration
• 63 nesting levels of parenthesized declarators within a full declarator
• 63 nesting levels of parenthesized expressions within a full expression
• 63 significant initial characters in an internal identifier or a macro name (each universal character name or extended source character is considered a single character)
• 31 significant initial characters in an external identifier (each universal character name specifying a short identifier of 0000FFFF or less is considered 6 characters, each universal character name specifying a short identifier of 00010000 or more is considered 10 characters, and each extended source character is considered the same number of characters as the corresponding universal character name, if any)
• 4095 external identifiers in one translation unit
• 511 identifiers with block scope declared in one block
• 4095 macro identifiers simultaneously defined in one preprocessing translation unit
• 127 parameters in one function definition
• 127 arguments in one function call
• 127 parameters in one macro definition
• 127 arguments in one macro invocation
• 4095 characters in a logical source line
• 4095 characters in a character string literal or wide string literal (after concatenation)
• 65535 bytes in an object (in a hosted environment only)
• 15 nesting levels for #included files
• 1023 case labels for a switch statement (excluding those for any nested switch statements)
• 1023 members in a single structure or union
• 1023 enumeration constants in a single enumeration
• 63 levels of nested structure or union definitions in a single struct-declaration-list

These are the minimum values a conforming C compiler must be able to handle.