Combine New String with C

string_combine.c

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

char* CombineNewString(char *w1,char *w2) 
{
    size_t count1,count2;
    int index;
    char *t,*t1,*t2;

    count1 = 0;
    count2 = 0;
    index = 0;
    t1 = w1;
    t2 = w2;

    while(*t1){
        count1++;
        t1++;
    }
    while(*t2){
        count2++;
        t2++;
    }
    t = (char*)malloc(sizeof(char) * (count1 + count2));
    for(size_t i = 0; i < count1; i++)
    {
        *(t + index) = *(w1 + i);
        index++;
    }
    for(size_t i = 0; i < count2; i++)
    {
        *(t + index) = *(w2 + i);
        index++;
    }

    *(t + index) = '\0';
    
    return t;
}

/*
output:
abcdef
*/
void main(void)
{
    char w1[] = "abc";
    char w2[] = "def";

    char *tt;
    tt = CombineNewString(w1,w2);

    printf("%s\n",tt);

    getchar();
}