Using OF Function in a Function

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in the ofApp.h

public:
float distance(int n,int valX, int valY);

in the ofApp.cpp

void ofApp::draw() {
    float dist = distance(1, 100, 200);
}

float ofApp::distance(int n, int valX, int valY) {
    float d;
    d = sqrt(((valY - mouseY) * (valY - mouseY)) + ((valX - mouseX) * (valX - mouseX)))
    return d;
}

instead of (1, 100, 200) you need to put your variables of course.