#include <stdio.h>

void cat_data(int *data1, const int *data2, int len2){
    int i = 0, j;
    while(data1[i] != NULL){
        i++;
    }
    for(j=0;j<len2;j++){
        *(data1+(i+j)) = data2[j];
    }
}

int main()
{
    int data1[7], data2[5], i, a;
    a=5;//data1[]に入れる最大の値
    for(i=0;i<7;i++){
        if(i<a){
            data1[i] = i + 1;
        }
        else{
            data2[i-a] = i + 1;
        }
    }
    int len2 = sizeof(data2) / sizeof(data2[0]);
    
    printf("before:\n");
    
    for(i=0;i<7;i++){
        if(i<a){
            printf("data1[%d] = %d\n",i,data1[i]);
        }
        else{
            printf("data2[%d] = %d\n",i-a,data2[i-a]);
        }
    }
    
    printf("len2 = %d\n",len2);
    
    cat_data(data1, data2, len2);
    
    printf("after:\n");
    
    for(i=0;i<7;i++){
        printf("data1[%d] = %d\n",i,data1[i]);
    }

    return 0;
}