Sizeof() varies with the same input

Question

void main()
{
printf("%d\n",sizeof('1'));
}

Output : 4

void main()
{
char a='1';
printf("%d\n",sizeof(a));
}

Output : 1

Can somebody say why it is different ?

Answer 1

In C, character literals are of type int.

Note that this was changed in C++, in which character literals have the obvious type char.

Answer 2

In C, character literals are of type int, in another word, sizeof('1') is the same as sizeof(int).

While sizeof(a) is the real sizeof(char).