Problem with changing numbers in an array in C

Question

First I generate some random numbers and then i need to exchange them like I discribte in the following lines. I tryed it iut with the for loobs.

I have to exchange the numbers of the array

Change number 1 and 2, 3 and 4,.....29 and 30
Change number 1 and 3, 4 and 7,.....27 and 30 Thank you for your Help

srand(time(NULL));
for ( i = 0; i < SIZE; i++ )
{
    mainArray[i] = rand() % ( UPPERBOUND - LOWERBOUND + 1 ) + LOWERBOUND;
}


for ( i = 0; i < SIZE; i++)
{

    if ( countDigitChange == 2 )
    {
        digitChanger1 = workArray2[i];
        i++;
        digitChanger2 = workArray2[i];
        workArray2[i] = digitChanger1;
        i--;
        workArray2[i] = digitChanger2;
        countDigitChange = 0;
    }
    countDigitChange++;
}
   for ( i = 0; i < SIZE; i++)
{
    if ( countDigitChange % 3 == 0 )
    {
        digitChanger1 = workArray3[i];
        i += 2;
        digitChanger2 = workArray3[i];
        workArray3[i] = digitChanger1;
        i += 2;
        workArray3[i] = digitChanger2;
        countDigitChange = 0;
    }
    countDigitChange++;
}

Are the numbers you mentioned already existing in the array? You say you need to "change" these numbers? What do you need to change them to? — Andreas Wenzel
– Andreas Wenzel, Commented Feb 24, 2021 at 20:03
You say you need to exchange these numbers? With what do you need to exchange them? — Andreas Wenzel
– Andreas Wenzel, Commented Feb 24, 2021 at 21:26

selbie · Accepted Answer · 2021-02-28 02:52:19Z

1

This seems much simpler:

Declare a helper function:

void swap_int(int* x, int *y)
{
    int tmp = *x;
    *x = *y;
    *y = tmp;
}

Then in your code that needs to shuffle the array:

int i, j; // declare this up top with all your other variable declarations

// for each pair of elements swap them
for (i=0, j=1; j < SIZE; i+=2, j+=2)
{
   swap_int(&mainArray[i], &mainArray[j]);
}

// swap array[0] with array[2], then swap array[3] with array[5], etc...
for (i=0, j=2; j < SIZE; i+=3, j+=3)
{
   swap_int(&mainArray[i], &mainArray[j]);
}

edited Feb 28, 2021 at 2:52

answered Feb 28, 2021 at 2:45

selbie

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