Calculating garbage value in case of overflow

Calculating garbage value in case of overflow

• 1.
  Calculating garbage value incase of Overflow
• 2.
  Garbage value inC  In a language like C, when you define a variable, like: int x;  A small block of memory is allocated to the variable. However, we have only declared the variable, and not initialized it, which means that the block of memory that has been allocated to the variable still contains some value that has been left over from previous programs and operations. That value is called a garbage value. This may lead to erroneous results in programs.  To avoid this, declare and initialize variables like this: int x = 0;
• 3.
  In case ofWindows  The space allocated for a variable of int datatype is 16 bits.  That means the maximum negative value that can be stored by the variable of int datatype is 2^15=-32768.  You may ask why 2^15 not 2^16.  This is because one bit is reserved for sign(+ or -)  Similarly the maximum +ve value that a variable of int datatype can store is 2^15-1=32767.  Why -1.Because 0 is also counted in case of +ve values.
• 4.
   Now letscome to long datatype.  The space allocated for a variable of int datatype is 32 bits. Maximum negative value= 2^31= -2147483648 Maximum +ve value= 2^31-1=2147483647  The space allocated for a variable of long datatype is 64 bits. Maximum negative value= 2^63= -9.22337e+18 Maximum +ve value= (2^63)-1= 9.22337e+18
• 5.
  Formula for calculatinggarbage value garbage value=overflow value-reference value. reference value is the value such that it is greater than the overflow value(neglecting the sign) obtained by the multiplication of the basic reference value by 2 until the value is greater than the overflow value(neglecting the sign) The sign of the reference value is same as that of overflow value. Basic reference value is 2^n where n represents the number of bits allocated. The garbage value thus calculated is checked whether it can fit the variable or not. If not the steps are repeated again.
• 6.
  Basic reference value=32768 sincethe reference value is less than the overflow value ,we have to multiply it by 2 i.e,32768*2=65536 65536 is greater than the 45000.That means reference value(RV)=65536.SInce RV must be of same sign,RV=+65536 1. now apply formula 2. garbage value=overflow value-reference value. 3. garbage value=45000-(+65536) 4. garbage value=-20536 5. -20536 comes within the limits of int datatype.
• 7.
  Lets understand whathappens. That means. OV=32768 Basic RV=32768. RV must be greater than OV. Therfore RV=32768*2=65536 Now, garbage value(GV)=OV-RV=32768-65536=-32768
• 8.
  Since both variablesa and b are assigned a value greater than their limits, when you run this program some garbage value will be the output.
• 9.
  2^31 RV>OV