Warnings for C programming

"Undetectable null bugs" from dead bytes:

The following code shows an example of a variable declared but not set to a value. Instead of returning the familiar "null", it returns what was left in the memory used for storing the variable, in this case, number 64:

// This is isolated code
int ghost;
printf("%d",ghost);
// This is console io
in  > Run code
out > 64

Turning negative mistakenly

printf() accesses data through the variable name, receives bytes, and converts them into specific formats, hence print"f". Sometimes there is a mismatch between the type of variable put into the printf() parenthesis and the %tag used in the string constant. In the following case:

// This is isolated code
unsigned int spook = 0xffffffff;
//4 Bytes are filled
printf("%d",spook);
printf("\n");
printf("%u",spook);

// This is console io
in  > Run code
out > -1
out > 4294967295

Any int divided by int results in int, oddly enough

The arithmatic operation of division for integers is defined as follows:

let p and q be two signed integers, at least one is negative
p%q =def= sign(p)*(abs(p)%abs(q))

let a and b ve two unsigned integers,
define a%b such that:
0 <= a%b < b
b*n <= a < b*(n+1)
b*n + a%b = a

define p/q such that:
q*(p/q)+p%q = p

This means things get tricky when there's a remainder, when p or q is negative or when both misfortunes are faced:

//Code
int p = 5;
int q = -2;

printf("%d",p/q);
printf("%d",p%q);

//Console
in  > Run Code
out > -2
out > 1

#define means Replacing with unexpected Danger

If a constant is defined in the #define part, don't set up variables of the same name. #define means thorough replacement!

// HEAD
#define PIG 233f

//Main, isolated code
float pig = 2024f

//console
in  > Run code
ERROR: 
main.c:x:xx: note: in expansion of macro 'PIG'
      |     float P = 0.001f;
      |           ^