trying to wrap my head around functions

So I know a bit about functions, yet for some reason I can't get my head to wrap around them. I understand they're used to split your program up to make it easier to deal with it, however I'm not completely understanding their workings. I have a runtime error with a certain function, not sure why. I wrote some code to experiment different ways of passing a function and what not.

Code:

---

#include <iostream>
#include <string>

using namespace std;

void function1(void);
void function2(void);
int returnfunc(void);
void str(string prompt);
string strFunc(string); // Problem function



int main()
{
    int num1;
    int num2;
    string strSent;

    function1(); // Call function1 in main

    function2(); // call function2 in main

    num2 = returnfunc(); // num2 will grab the value that returnfunc returns within its function

    cout << "The number you passed to main was " << num2 << endl << endl; // shows that nb1 successfuly returns a value and assigns it to the variable 'num2'

    str("The prompt is within the () of this function"); // the message determined from prompt is defined here
    cout << endl << endl;

    cout << "Enter a sentence.\n";
    cin.get();
    getline(cin, strSent);

    // Problem here
    strFunc(strSent);




    return 0;
}

void function1()
{
    cout << "Calling this function in main() will display this stream." << endl << endl;
}

void function2()
{
    int n1;

    cout << "Enter a number -> ";
    cin >> n1;

    cout << "The number you entered was \"" << n1 << "\"" << endl << endl;
}

int returnfunc()
{
    int nb1;

    cout << "Enter a number to pass to main ";
    cin >> nb1;

    return nb1;
}

void str(string prompt)
{
    cout << prompt; // will display whatever prompt you code in the main
}

string strFunc(string strsnt) // problem here
{
    cout << strsnt;
}

---

Perhaps someone can elaborate more on them? Maybe some more practical approaches?

Your strFunc function is declared as "function returning string", yet you do not. You must do so, and your compiler has been jumping up and down frantically trying to tell you so this whole time (so in future you should listen to it).

Yeah I realized that not even 30 seconds ago of making this reply. So this is how I understand functions...

int functionName(int, double, char, string)

Where int is gonna be the returned data type, functionName is the name of the function and the types within the () are the variables that will be used within the function, and the arguments needed when calling the function?

That is all correct.

So if I don't want to use arguments when I call the function, i must leave () for (void) and declare the arguments within the function... all about scoping. the () is the parameter list correct?

edit: Through further experimenting, I found something else which causes me some confusion.

Code:

---

int numInFunc(int somenum)
{
    somenum = 1234;

    return somenum;

... in main()
...
    numInFunc(num1);

    cout << "The number from the function numInFunc is: " << num1 << endl;
...
}

---

The main code doesn't give me the correct number. However if I rewrite it like this and put the function in the output stream

Code:

---

    cout << "The number from the function numInFunc is: " << numInFunc(num1) << endl;

---

It gives me the correct number. The variable num1 does not hold the value when I put it inside the function argument list to take it, then output the value the variable holds later?

Quote:

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Originally Posted by Darkroman

The variable num1 does not hold the value when I put it inside the function argument list to take it, then output the value the variable holds later?

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When you make that function call, somenum is a copy of num1, so assigning to somenum has no effect on num1. If you had made somenum a reference to int instead, then somenum would be an alias of num1, hence assigning to somenum would have changed num1.