CODEWITHSUNDEEP
cmultidimensional-array
jrstevens
jrstevens

Reputation: 33

Loop through a nested loop two-by two in C

I would like to loop through two arrays in a semi-zipped fashion, such that for as many entries as possible, the following pattern is observed:

arr1[i]   arr2[j]
arr1[i]   arr2[j+1]
arr1[i+1] arr2[j+2]
arr1[i+1] arr2[j+3]
....

For example, if len arr1 is 96 and len arr2 is 3, I would like to see

0 0
0 1
1 2
1 0
2 1
2 2
3 0
3 1
4 2
4 0
5 1
5 2

I'm having a little trouble getting the logic exactly right; any help would be greatly appreciated

Upvotes: 0

Views: 119

Answers (2)

Travis
Travis

Reputation: 2188

Pseudocode:

i = 0;
for (x = 0; i < arr1.len; ++x) {
    i = x / 2;  // integer division
    j = x % arr2.len;
    // use arr1[i] and arr2[j]
}

Use integer division to repeat a value multiple times before moving on to the next value (e.g. 0 0 1 1 2 2 3 3 ...), where the number of times you want to repeat a value is equal to the denominator.

Use modulo division to repeat a sequence of values indefinitely (e.g. 0 1 2 0 1 2 0 1 2 ...), where the number of items in the sequence is equal to the denominator.

Upvotes: 4

Vlad from Moscow
Vlad from Moscow

Reputation: 310980

If I have understood you correctly you need a loop like the one shown in the demonstrative program below.

#include <stdio.h>

#define N 10
#define M 3

int main( void )
{
    int a[N];
    int b[N];

    for ( int i = 0; i < N; i++ ) a[i] = i;
    for ( int i = 0; i < M; i++ ) b[i] = i;

    for (int i = 0, j = 0, k = 1; i < N; i += k ^= 1, j = ( j + 1 ) % M)
    {
        printf( "%d %d\n", a[i] , b[j] );
    }
}

The program output is

0 0
0 1
1 2
1 0
2 1
2 2
3 0
3 1
4 2
4 0
5 1
5 2
6 0
6 1
7 2
7 0
8 1
8 2
9 0
9 1

Upvotes: 0

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