How do I merge two arrays having different values into one array?

Question

Suppose you have one array a[]=1,2,4,6 and a second array b[]=3,5,7. The merged result should have all the values, i.e. c[]=1,2,3,4,5,6,7. The merge should be done without using functions from <string.h>.

Answer 1

I haven't compiled and tested the following code, but I am reasonably confident. I am assuming both input arrays are already sorted. There is more work to do to make this general purpose as opposed to a solution for this example only. No doubt the two phases I identify could be combined, but perhaps that would be harder to read and verify;

void merge_example()
{
    int a[] = {1,2,4,6};
    int b[] = {3,5,7};
    int c[100];     // fixme - production code would need a robust way
                    //  to ensure c[] always big enough
    int nbr_a = sizeof(a)/sizeof(a[0]);
    int nbr_b = sizeof(b)/sizeof(b[0]);
    int i=0, j=0, k=0;

    // Phase 1) 2 input arrays not exhausted
    while( i<nbr_a && j<nbr_b )
    {
        if( a[i] <= b[j] )
            c[k++] = a[i++];
        else
            c[k++] = b[j++];
    }

    // Phase 2) 1 input array not exhausted
    while( i < nbr_a )
        c[k++] = a[i++];
    while( j < nbr_b )
        c[k++] = b[j++];
}

Answer 2

I am learning c myself at them moment, so don't take this as the perfect solution, but maybe you can get some ideas from what I did to solve your own problem.

#include <stdio.h>
#include <stdlib.h>

int compare (const void * first, const void * second){
    return  *(int*)first - *(int*)second ;
}

int main(){
    int a[] = {1,2,4,6};
    int b[] = {3,5,7};
    size_t sizeA =sizeof(a)/sizeof(a[0]);
    size_t sizeB = sizeof(b)/sizeof(b[0]); 
    size_t sizeC = sizeA + sizeB; 
    /*allocate new array of sufficient size*/
    int *c = malloc(sizeof(int)*sizeC);
    unsigned i;
    /*copy elements from a into c*/
    for(i = 0; i<sizeA; ++i){
        c[i] = a[i];
    } 
    /*copy elements from b into c*/
    for(i = 0; i < sizeB; ++i){
        c[sizeA+i] = b[i];
    }
    printf("array unsorted:\n");
    for(i = 0; i < sizeC; ++i){
        printf("%d: %d\n", i, c[i]);
    }
    /*sort array from smallest to highest value*/
    qsort(c, sizeC, sizeof(int), compare);
    printf("array sorted:\n");
    for(i = 0; i < sizeC; ++i){
        printf("%d: %d\n", i, c[i]);
    }
    return 0;
}