How to use size of operators in c language

#include<stdio.h>
int main()
{
    int var;
    printf("size of int =%u\n",sizeof(int));
    printf("size of float=%u\n",sizeof(float));
    printf("size of var=%u\n",sizeof(var));
    printf("size of an integer constant=%u\n",sizeof(45));
    return 0;

}