2's complement of a binary number in c language?

Answer 1

/* note that neither of these functions have been tested, so there may be typos and the like */

/* if you're looking to return a real value: */
unsigned int complement(unsigned int value){
unsigned int returnvalue = 0;
while(value){

returnvalue <<= 1;
returnvalue += !(value & 1);
value >>= 1;

}
return returnvalue;

}

/* if you're looking for a string representing the binary number: */
char *complement(unsigned int value){
int numchars = 8 * sizeof(unsigned int);
int n;
char *returnvalue = malloc((numchars + 1) * sizeof(char));

for(n = 0; n < numchars; n++){
if(value & (1 << (numchars - 1 - n))){
returnvalue[n] = '1';

}else{
returnvalue[n] = '0';

}

}
returnvalue[numchars] = (char)NULL;

return returnvalue;

}