c set value of a var from pointer code example

Example 1: how to use a pointer as a parameter in c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
void add(int* a, int* b, int* c)
{
    *c = *a + *b;
}
int main()
{
	int a, b, c;
	a = 3;
	b = 5;
	add(&a, &b, &c);
	printf("%d", c);
}

Example 2: Assign integer value to pointer?

int main(){
    int variable;
    int *ptr = &variable;
    *ptr = 20;
    printf("%d", *ptr);
    return 0;
}