Thread: arrays of int, parsing, changing one element

Dear Fellow coders

I have an array of integers in main() and all elements are given a zero value
int counts[10] = {0,0,0,0,0,0,0,0,0,0}

I am parsing a pointer to this array to another function:
anotherfuntion(counts);

1) void anotherfunction(int *num)
2) {
3) (num)++; /*Compiles without messages but does not increment value to one*/
4) printf(“%d”, *num); /*Prints zero*/
5) }
from within anotherfunction() I want to increment the value in element 0, (counts[0]) by one and then print it out. So far this has not worked.

I have tried reading my original study manual, but this does not include an example of incrementing the value inside an element using “++”. It shows how to move along the array using pointer arithmetic.

I have also tried many variations as follows:
*num++;
*(num)++;
(*(num)++);
*num+0++;
*(num+0)++;
(*num+0)++;
These produce a message “L value required”. My compiler says “An lvalue is an object locator: an expression that designates an object. An example of an lvalue expression is *P, where P is any expression evaluating to a non-null pointer.
A modifiable lvalue is an identifier or expression that relates to an object that can be accessed and legally changed in memory.”
Wow. However, I am sorry to say I do not properly understand this.

I have performed a step through/watch and seen that line 3 does not increment element zero.

I am using Borlands DOS Turbo C++ V 3.0 complier

Any help or guidance appreciated

Stephanos

You must dereference the pointer first - then you can increment the value the pointer is pointing at.
The following code works fine with Borland Command Line Tools 5.5.1.

Code:

#include <stdio.h>

void func(int *num);

int main()
{
    int array[10] = {0};

    func(array);
	
    return 0;
}

void func(int *num)
{
    (*num)++;
    printf("%d", *num);
}

If you want to change other elements in the array you need to pass the number of elements in the array:

Code:

#include <stdio.h>

void func(int *array, int nofelements);

void func(int *array, int nofelements)
{
   int i;
   for(i = 0; i < nofelements; i++)
      array[i] = i;
}

int main(void)
{
   int i;
   int array[10] = {0,0,0,0,0,0,0,0,0,0};

   func(array, sizeof(array)/sizeof(*array));

   for(i = 0; i < sizeof(array)/sizeof(*array); i++)
      printf("array[%d] = %d\n", i, array[i]);

   return 0;
}