int a=-5; Here variable a is by default signed int. unsigned int b=-5u; Constant -5u will convert into unsigned int. Its corresponding unsigned int value will be : 65536 – 5 + 1= 65532 So, b = 65532 In any binary operation of dissimilar data type for example: a == b Lower data type operand always automatically type casted into the operand of higher data type before performing the operation and result will be higher data type. In c signed int is higher data type than unsigned int. So variable b will automatically type casted into signed int. So corresponding signed value of 65532 is -5 Hence, a==b