Function Declaration and Invocation

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#include <iostream>

using namespace std;
//function prototype
void helloWorld(); //Void function

//value-returning functions
int addNum(int,int);
int subNum(int,int);
int mulNum(int,int);
int divNum(int,int);

int main()
{
    cout<<"Hello World!\n";
    helloWorld();
    int a,b;
    a = 10;
    b = 20;
    cout<<"Addition:"<<addNum(a,b)<<endl;
    cout<<"Subtraction:"<<subNum(a,b)<<endl;
    cout<<"Multiplication:"<<mulNum(a,b)<<endl;

    return 0;
}

void helloWorld(){
    cout<<"Hellow p0wzxc"<<endl;
}

int addNum(int a,int b){
    return a + b;
}

int subNum(int a,int b){
    return a - b;
}

int mulNum(int a,int b){
    return a * b;
}
int divNum(int a,int b){
    return a / b;
}