Operations of the elements of arrays in a function' c++ - c++

Question

Can I operate the elements of an array in a function(in the parameter)?
float f(i, u, v)
{
if (i == 1) {
return (u - v); //example of the returned value
}
if (i == 2) {
return (u + v);
}
}
int main()
{
int i;
float x[3],y1,y2,h;
x[1]=1;//value of the first element of x[m]
x[2]=1;
h=0.01;
for (i = 1; i <= 2; i++) {
y1=h * f(i, x[1], x[2]);
y2=h * f(i, x[1] + y1/2, x[2]+y1/2);
y3=h* f(i,x[1] + y2/2, x[2]+y2/2);
y4=h * f(i,x[1] + y3, x[2]+y3);
x[1]=x[1] + (y1+ 2 * y2 + 2 * y3+2 * y4)/ 6;
x[2]=x[2] + (y1+ 2 * y2 + 2 * y3+2 * y4)/ 6;
cout<<x[1]<<endl;
}
}
with:
x[1] and x[2] are the elements of the array x[m]
How can I operate elements of different arrays in parameter?

Answer 1

I would recommend you to try to compile your code, the compiler will give you some important hints as of what is wrong. Here is the code compiled online.
To make it compile i changed it to this:
#include <iostream>
using namespace std;
float f(int i, float u, float v) {
if (i == 1) {
return (u - v); // example of the returned value
}
// if (i == 2) { // This if-statement is not needed
return (u + v);
// }
}
int main() {
int i;
float x[3] = {0, 1, 1}; // x[0] is unused...?
float y1 = 0;
float y2 = 0;
float y3 = 0;
float y4 = 0;
const float h = 0.01;
for (int i = 1; i <= 2; i++) {
y1 = h * f(i, x[1], x[2]);
y2 = h * f(i, x[1] + y1 / 2, x[2] + y1 / 2);
y3 = h * f(i, x[1] + y2 / 2, x[2] + y2 / 2);
y4 = h * f(i, x[1] + y3, x[2] + y3);
x[1] = x[1] + (y1 + 2 * y2 + 2 * y3 + 2 * y4) / 6;
x[2] = x[2] + (y1 + 2 * y2 + 2 * y3 + 2 * y4) / 6;
cout << x[1] << endl;
}
}
Note the changes
You need to specify the types for the variables in the function f(...)
You need to define all variables before using them (a good rule is to specify everything right before you use it, and add const if not changed.
Remember to zero initialize variables that you are going to add to (y1, y2... etc)
Also I would recommend you to use x1 instead of x1, since you are mixing styles between x and y, and you are not using the zeroeth element. Like this
int main() {
int i;
float x1 = 1;
float x2 = 2;
float y1 = 0;
float y2 = 0;
float y3 = 0;
float y4 = 0;
const float h = 0.01;
for (int i = 1; i <= 2; i++) {
y1 = h * f(i, x1, x2);
y2 = h * f(i, x1 + y1 / 2, x2 + y1 / 2);
y3 = h * f(i, x1 + y2 / 2, x2 + y2 / 2);
y4 = h * f(i, x1 + y3, x2 + y3);
x1 = x1 + (y1 + 2 * y2 + 2 * y3 + 2 * y4) / 6;
x2 = x2 + (y1 + 2 * y2 + 2 * y3 + 2 * y4) / 6;
cout << x1 << endl;
}
}