C++ signed和unsigned 大小比较

<span style="font-family: Arial, Helvetica, sans-serif;"><span style="font-size:14px;">using namespace std;</span></span>

<span style="font-size:14px;">
int main() {
unsigned int  a = -1;
int b = 0;
if (a > b){

cout << "hello\n";
}else{
cout << "111111\n";
}
cout  << "test\n";
return 0;
}</span></span>

如上图所示输出为 hello ;a与b比较的时候，a会自动转换成unsigned int类型进行比较。由于signed int的负数最高位是1，转换成unsigned int之后，就会变成一个很大的unsigned int型正数，所以a与b比较时a会大于b。所以会输出hello；