Changing the value of something in a function

Question

This is a test case for something larger, which is why it is written the way is. How could I make this bit of code so that a's value would keep incrementing? In my project I call a function that parses a line from a file. I need to set values of a struct to certain values that were set in the function call (the parameters of the function were initialized in the main function, like the code below).

int increment(int a)
{
    a++;
    return 0;
}
int main()
{
    int a =0;
    int b =0;
    while( b<5){
        increment(a);
        b++;
        cout << "a is: " << a << ". And b is: " << b << "\n";
    }
    system("PAUSE");
}

Thanks.

In many situations, you would be better off returning the incremented value, as in `int increment(int a) {return a+1;}`. The you call it as `a = increment(a)`. — Sergey Kalinichenko, Feb 10 '13 at 01:22

Lews Therin · Answer 1 · 2013-02-10T01:34:00.957

3

Pass its address to increment

void increment(int *a){
  (*a)++;  
}
increment(&a);
//Using the address of operator pass in the address of a as argument

edited Feb 10 '13 at 01:34

answered Feb 10 '13 at 01:18

Lews Therin

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@Lewis Therin Isn't this just incrementing the pointer; not the value? – Richard Schneider Feb 10 '13 at 01:31
@RichardSchneider Operator precedence? You could be right I haven't done C in ages. I've put the bracket to be explicit. – Lews Therin Feb 10 '13 at 01:34

score 1 · Answer 2 · edited May 23 '17 at 12:27

1

You could use a pointer: See Passing by reference in C for a similar question.

Also, you could just modify your increment function to return the incremented value of a, and call it in main like the following:

a = increment(a);

edited May 23 '17 at 12:27

Community

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answered Feb 10 '13 at 01:31

ChrisC

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score 0 · Answer 3 · answered May 26 '17 at 19:16

0

You could:

Declare static int a = 0; return a++;
Change the signature to int increment( int* a ) and return *a++;
Declare a in file scope of the same source file as increment()
Make a global
Do this in C++ and pass a by reference

answered May 26 '17 at 19:16

Davislor

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score -1 · Answer 4 · edited May 26 '17 at 19:01

-1

You are passing a by value, so the value of a can never be changed.

One solution is:

int increment (int a) { return a + 1; }

Then in your loop:

a = increment(a);

Another solution is to pass a by reference (a pointer)

void increment (int *a) { *a = *a + 1; }

and in the loop

increment(&a);

edited May 26 '17 at 19:01

BLUEPIXY

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answered Feb 10 '13 at 01:23

Richard Schneider

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2nd version of `increment` was wrong and have now updated it. – Richard Schneider Feb 10 '13 at 01:29

Changing the value of something in a function

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