Forgotten rules of C/C++: Part 1

Following is a list of important points people find very convenient to forget. This is the first article of a series

·   For bitwise operations, operand is promoted to "int" before evaluation.

unsigned char I = 0x80;
printf("%d", i<<1 nbsp="nbsp">  256

·   printf(5 + "intelligent");  => “ligent”

      Number specifies displacement to string pointer. This is the same as doing…

char *s = "intelligent";
s += 5;
printf("%s",s);

·    In a switch statement, initializations are allowed in the beginning, but they are NOT EXECUTED. The control is passed directly to an executable statement, i.e. matching case statement.

switch(1)
{
     printf("hello");                         => NOT PRINTED
     case 1:printf("case 1");break;
     case 2:printf("case 2");break;
}

·   The ++ operator means ``add one to a variable'' and DOES NOT work with constants.

int i = ++ 3 ;
printf("%d", i);                              =>  GARBAGE VALUE

·   Static arrays are constant! The base address cannot be modified. Any pointer arithmetic that attempts to do so causes a compilation error.

int arr[ 10 ] ;                     => “arr” is a constant. It is defined to be the address, &arr[ 0 ].

·   Array pointer logic for an array, “int a[10][10];”

      a+1
=> a[1]
=> &a[1][0]

·    In pointer arithmetic, addition and subtraction are valid operations, (as long as they don’t try to change the base address of the pointer) but pointer division and pointer multiplication are INVALID.