C Programming Questions and Answers – Pointers and Function Arguments.c

The same question:
What will be the output of the following C code?

Question 1:

//   Date:2020/3/29
//   Author:xiezhg5
#include <stdio.h>
void foo(int*);
int main(void)
{
	int i=10,*p=&i;
	foo(p++);
}
void foo(int*p)
{
	printf("%d\n",*p);
}

//Answer: 10

Question 2:

//   Date:2020/3/29
//   Author:xiezhg5
#include <stdio.h>
void foo(int *p);
int main(void)
{
	int i=97,*p=&i;
	foo(&i);
	printf("%d\n",*p);
}
void foo(int *p)
{
	int j=2;
	p=&j;
	printf("%d ",*p);
}

//Answer:2 97

Question 3:

//   Date:2020/3/29
//   Author:xiezhg5
#include <stdio.h>
void foo(int **p);
int main(void)
{
	int i=97,*p=&i;
	foo(&p);
	printf("%d\n",*p);
	return 0;
}
void foo(int **p)
{
	int j=2;
	*p=&j;
	printf("%d ",**p);
}

//Answer:2 2

Question 4:

//   Date:2020/3/29
//   Author:xiezhg5
#include <stdio.h>
void foo(int **p);
int main(void)
{
	int i=10;
	int *const p=&i;
	foo(&p);
	printf("%d\n",*p);
}
void foo(int **p)
{
	int j=11;
	*p=&j;
	printf("%d ",**p);
}

//Answer:11 11

Question 5:

//   Date:2020/3/29
//   Author:xiezhg5
#include <stdio.h>
void foo(int **p);
int main(void)
{
	int i=10;
	int *p=&i;
	foo(&p);
	printf("%d ",*p);
	printf("%d ",*p);
}
void foo(int **const p)
{
	int j=11;
	*p=&j;
	printf("%d ",**p);
}

//Answer:11 11 Undefined-value

Pointers to functions
A pointer to function can be initialized with an address of a function. Because of the function-to-pointer conversion, the address-of operator is optional:

void f(int);
void (*pf1)(int) = &f;
void (*pf2)(int) = f; // same as &f

Unlike functions, pointers to functions are objects and thus can be stored in arrays, copied, assigned, passed to other functions as arguments, etc.
A pointer to function can be used on the left-hand side of the function call operator; this invokes the pointed-to function:

#include <stdio.h>
int f(int n)
{
    printf("%d\n", n);
    return n*n;
}
int main(void)
{
    int (*p)(int) = f;
    int x = p(7);
}

Dereferencing a function pointer yields the function designator for the pointed-to function:

int f();
int (*p)() = f;    // pointer p is pointing to f
(*p)(); // function f invoked through the function designator
p();    // function f invoked directly through the pointer

Equality comparison operators are defined for pointers to functions (they compare equal if pointing to the same function).
Because compatibility of function types ignores top-level qualifiers of the function parameters, pointers to functions whose parameters only differ in their top-level qualifiers are interchangeable:

int f(int), fc(const int);
int (*pc)(const int) = f; // OK
int (*p)(int) = fc;       // OK
pc = p;                   // OK

Reference:https://en.cppreference.com/w/c/language/pointer