Some usage of sizeof

Code:

#include<stdio.h>
#include<string.h>
char foo()
{
	printf("foo() has been called.\n");
	return 'a';
}
/*void foo3(char a3[3])
{
	int c3 = sizeof( a3 ); // c3 == 
	printf("c3=sizeof( a3 )=%d\n",c3);
}
void foo4(char a4[])
{
	int c4 = sizeof( a4 ); // c4 == 
	printf("c4=sizeof( a4 )=%d\n",c4);
}*/

/*mian function*/
int main()
{
	int n;
	n = 10; 
	char ary[n];		   
	printf("sizeof(ary)       =%d\n", sizeof(ary)); // ok. output: 10
	
	size_t sz = sizeof( foo() );	// The type return value of the foo()is char,
									//besides sz=sizeof(char),foo()Will not be called
	printf("sizeof( foo() )   =%d\n", sz);
	
	/*****************************Data Type*****************************************************/
	printf("sizeof(char)         =%d\n",sizeof(char));
	printf("sizeof(signed char)  =%d\n",sizeof(signed char));
	printf("sizeof(unsigned char)=%d\n",sizeof(unsigned char));
	printf("sizeof(int)          =%d\n",sizeof(int));
	printf("sizeof(signed int)   =%d\n",sizeof(signed int));
	printf("sizeof(unsigned int) =%d\n",sizeof(unsigned int));
	printf("sizeof(float)        =%d\n",sizeof(float));
	printf("sizeof(double)       =%d\n",sizeof(double));
	
	/******************************point**********************************************************/
	char *pc = "abc";
	int *pi;
	//string * ps;
	char **ppc = &pc;
	void (*pf)();// 
	printf("sizeof(pc)          =%d\n",sizeof(pc)); //4
	printf("sizeof(pi)          =%d\n",sizeof(pi)); //4
	//sizeof( ps ); // 
	printf("sizeof(ppc)         =%d\n",sizeof(ppc)); //4
	printf("sizeof(pf)          =%d\n",sizeof(pf));// 4
	
   /***********************Array*****************************************************************/ 
	char a1[] = "abc";
	int a2[3];
	printf("sizeof(a1[])     =%d\n",sizeof(a1));// 4
	
	printf("sizeof(a2[])     =%d\n",sizeof(a2[3]));//3*4=12(attach to int)
	
	/*Calculate the numbers of the array*/
	
	int c1; //  Total length / length of a single element
	printf("c1= sizeof( a1 ) / sizeof(char) =%d\n",c1= sizeof( a1 ) / sizeof( char )); 
	int c2;//   Total length / length of the first element
	printf("c2= sizeof( a1 ) / sizeof(a1[0])=%d\n",c2 = sizeof( a1 ) / sizeof( a1[0] ));
	//printf("c4=sizeof( a2 )=%d\n",foo4(a2));
	
	/******************************Structure*****************************************************/
	struct S1
	{
		char c;
		int i;
	};
	printf("sizeof(S1)=%d\n",sizeof(struct S1));
	struct S2
	{
		int i;
		char c;
	};
	printf("sizeof(S2)=%d\n",sizeof(struct S2));
	struct S3
	{
		char c1;
		S1 s;
		char c2;
	};
	printf("sizeof(S3)=%d\n",sizeof(struct S3));
	
	/*************************************Bit field****************************************************/
	struct BF1
	{
		char f1 : 3;
		char f2 : 4;
		char f3 : 5;
	};
	printf("sizeof(BF1)=%d\n",sizeof(struct BF1));
	union U
	{
		int i;
		char c;
		S1 s;
	};
	printf("sizeof(U)=%d\n",sizeof(U));
	return 0;
}

Welcome to give some constructive suggestions!
Thank you!

 

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