Custom function---->ADD routine description

//Addition operation, call ADD custom function routine description: (function divided into 1. library function; 2. custom function)
//int main()
//{
// int x = 10;
// int y = 20;
// int sum = 0;
// int a = 100; //I want to calculate multiple addition results at the same time, so the writing is too bloated
// int b = 200;
// //sum = x + y;
/ / sum = add(x, y);//Custom function name, perform addition operation.
// //Function writing in mathematics: 1.f(x)=2x+12.f(x,y)=x+y
// //sum = a + b;
// sum = add(a, b );
// printf("sum=%d\n", sum);
// return 0;
//int add(intx, inty) //ADD expression;
//{
// int z = x + y;
// return 0;
//}
//}