波浪号（~）运算符有什么作用？

Question

I recently saw the above operator in a code,I googled for it but found nothing.The code is below.Please describe what actually does this operator do?

#include<stdio.h>
int main()
{
    unsigned long int i=0;
     char ch;
    char name1[20],name2[20];
    FILE *fp,*ft;
    printf("ENTER THE SOURCE FILE:");
    gets(name1);
    printf("ENTER THE DESTINATION FILE:");
    gets(name2);
    fp=fopen(name1,"r");
    ft=fopen(name2,"w");
    if(fp==NULL)
    {
        printf("CAN,T OPEN THE FILE");
    }
    while(!feof(fp))
    {
         ch=getc(fp);
         ch=~((ch^i));/*<--Here*/
        i+=2;
        if(i==100000)
        {
             i=0;
        }
     putc(ch,ft);
    }
    fclose(fp);
    fclose(ft);
    return 0;
}       

Answer 1

The ~ operator in C++ (and other C-like languages like C and Java) performs a bitwise NOT operation - all the 1 bits in the operand are set to 0 and all the 0 bits in the operand are set to 1. In other words, it creates the complement of the original number.

For example:

10101000 11101001 // Original  (Binary for -22,295 in 16-bit two's complement)
01010111 00010110 // ~Original (Binary for  22,294 in 16-bit two's complement)

In your example, ch=~((ch^i)) performs a bitwise NOT on the bitwise XOR of ch and i then assigns the result to ch .

The bitwise NOT operator has an interesting property that when applied on numbers represented by two's complement , it changes the number's sign and then subtracts one (as you can see in the above example).

You may want become familiar with the different operators of the C++ language since it is difficult to search for operators on search engines. Better yet, you can get a good C++ book which will tell you about the C++ operators.

Answer 2

The ~ operator inverts all the bits. So 10000001 becomes 01111110 .

Answer 3

It is the bitwise complement operator. Given the input

010011101

returns the output:

101100010