How to use size of operator 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;
}