Changing value in memory address

#include <iostream>

int main() {
        int intvar = 5;
        printf("address of intvar = %p\n", (void *)(&intvar));
        printf("address of intvar - 1 = %p\n", (void *)(&intvar - 1));
        printf("address of intvar + 1 = %p\n", (void *)(&intvar + 1));

        uintptr_t z = uintptr_t(&intvar);
        unsigned short *addr = (unsigned short *)z;
        *addr = 100;

        uintptr_t p = uintptr_t(&intvar);
        int value = *reinterpret_cast<int *>(p);

        printf("value of address = %d\n", value);

        system("pause");
        return 1;
}