c++ string -=

There is no such operator as `string -=` in C. The `-=` operator is used for arithmetic operations on numeric variables, but it cannot be used with strings.

If you want to remove a substring from a C string, you need to use string manipulation functions such as `strstr()` and `strcpy()`. For example, you can use `strstr()` to find the position of the substring you want to remove, and then use `strcpy()` to copy the remaining part of the string to a new location.

Here's an example code snippet that removes a substring from a C string:

#include <stdio.h>
#include <string.h>

int main() {
    char str[] = "Hello world!";
    char substr[] = "world";
    
    char* pos = strstr(str, substr); // Find the position of the substring
    
    if (pos != NULL) {
        strcpy(pos, pos + strlen(substr)); // Copy the remaining part of the string
    }
    
    printf("%s\n", str); // Output: "Hello !"
    
    return 0;
}