#include <stdio.h>
 
void cat_data(int *data1, const int *data2, int len2) {
 
    for (int i = 0; i < len2; i++) {
        data1[7+ i] = data2[i];
    }
}
 
int main(void) {
 
    int data1[12] = {1, 2, 3, 4, 5, 6, 7};
    int data2[5]  = {3, 4, 5, 6, 7};
 
    int len2 = sizeof(data2) / sizeof(data2[0]);
 
    cat_data(data1, data2, len2);
 
    for (int i = 0; i < 7 + len2; i++) {
        printf("data1[%d] = %d\n", i, data1[i]);
    }
 
    return 0;
}
 

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