To pass values into the function is done by the two ways

Pass values into the function also known as call by value

Pass its reference also known as call by reference

In the first approach the value is directly passed into the function

* C Program to swap two numbers using pointers and function. */
#include <stdio.h>
void swap(int a,int b);
int main(){
  int num1=5,num2=10;
  swap(num1,num2);  /* value of num1 and num2 is passed to swap function */
  printf("Number1 = %d\n",num1);
  printf("Number2 = %d",num2);
  return 0;
}
void swap(int a,int b){ 
  int temp;
  temp=a;
  a=b;
  b=temp;
}

Actual values are passed into the function for swapping the numbers.

And in the second approach the reference are passed instead of the values into the function as an argument.

* C Program to swap two numbers using pointers and function. */
#include <stdio.h>
void swap(int *a,int *b);
int main(){
  int num1=5,num2=10;
  swap(&num1,&num2);  /* address of num1 and num2 is passed to swap function */
  printf("Number1 = %d\n",num1);
  printf("Number2 = %d",num2);
  return 0;
}
void swap(int *a,int *b){ /* pointer a and b points to address of num1 and num2 respectively */
  int temp;
  temp=*a;
  *a=*b;
  *b=temp;
}