gistfile1.cpp

#include <stdio.h>

int main(){
    unsigned char a = 255;
    unsigned long int b = (a << 24);
    unsigned long int c = ((unsigned long int) a << 24);

    printf("b=%lu\n", b);
    printf("c=%lu\n", c);
    return 0;
}

cypreess@iMac ~ g++ f.cc -o f && ./f
b=18446744073692774400
c=4278190080