Why is the size of the data type different when the value is directly passed to the sizeof operator?

Question

#include <stdio.h>
int main() {
    char a = 'A';
    int b = 90000;
    float c = 6.5;
    printf("%d ",sizeof(6.5));
    printf("%d ",sizeof(90000));
    printf("%d ",sizeof('A'));
    printf("%d ",sizeof(c));
    printf("%d ",sizeof(b));
    printf("%d",sizeof(a));
    return 0;
}

The output is:

8 4 4 4 4 1

Why is the output different for the same values?

Answer 1

Constants, like variables, have a type of their own:

• 6.5 : A floating point constant of type double
• 90000 : An integer constant of type int (if int is 32 bits) or long (if int is 16 bits)
• 'A' : A character constant of type int in C and char in C++

The sizes that are printed are the sizes of the above types.

Also, the result of the sizeof operator has type size_t. So when printing the proper format specifier to use is %zu, not %d.