C language beginners-questions about pointer as a parameter and changing its value

Example 1:
[Cpp]
# Include <stdio. h>
Int f (int * p ){
P = p + 1;
Return printf ("% d \ n", * p );
}
Void main (){
Int a [] = {1, 2 };
Int * p = a; // the pointer p is the first address.
F (p); // call
Printf ("% d", * p); // The value of p will not change.
}

 
Result:
2
1
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Example 2:
[Cpp]
# Include <stdio. h>
Void z (int * p ){
P = p + 1;
* P = 100;
}
Void mian (){
Int a [] = {1, 2 };
Int * p =;
Z (p); // call
Printf ("a [1] = % d", * (p + 1); // the value in the memory space pointed to by the pointer (p + 1) has changed
}

 
Result:
A [1] = 100
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Through the above two examples, we can conclude that when a pointer is passed as a parameter, its value cannot be changed in other functions (the address pointed by this pointer), but it can be changed.
The value in the address.
So to realize the value exchange between the two first-level pointers, we need to use the second-level pointer: (pointer q points to a, pointer p points to B, implement q points to B, p points to)
[Cpp]
# Include <stdio. h>
Void exchange (int ** x, int ** y ){
Int * temp;
Temp = * x; // * x = * qq = &
* X = * y;
* Y = temp;
}
 
Void main (){
Int a = 100;
Int B = 12;
// Define the pointer
Int * q = &;
Int * p = & B;
Int ** qq = & q;
Int ** pp = & p;
// Output
Printf ("q = % p \ n", q );
Printf ("p = % p \ n", p );
// Call the function for conversion
Exchange (qq, pp );
 
Printf ("========= changed ===============\ n ");
Printf ("q = % p \ n", q );
Printf ("p = % p \ n", p );
}

Result:
Q = 0012FF44
P = 0012FF40
========= After the change ==========
Q = 0012FF40
P = 0012FF44
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