Concatenate and show on screen

Question

I don’t know how to print the strcat on the screen, I don’t know how to concatenate to the position typed in the scanf_s.

int main() {

    char string1[10], string2[10];
    int RU[1];
    char NomeSobrenome;

    printf("digite o Nome\n");
    gets_s(string1);

    printf("Digite o segundo nome\n");
    gets_s(string2);

    printf("Digite o ultimo digito do RU");
    scanf_s("%d", &RU[1]);

    strncat(string1, string2,RU[1]);

    NomeSobrenome = strncat;

    printf("%c", NomeSobrenome);

}

Answer 1

strncat concatenates one string at the end of the other, not in the middle.

You can use strcpy to copy the string2 entire to the desired memory position, so just manipulate that position within the string1

printf("Digite o ultimo digito do RU\n");
scanf("%d", &i);

strcpy(&string1[i], string2);
printf("%s", string1);

Note that this method is not safe, because string1 stores only 10 characters, the ideal would be to create a string that can store as much string1 and string2

int main() {
    char string1[10], string2[10], string3[20];
    int i;

    printf("digite o Nome\n");
    scanf("%s9", string1);

    printf("Digite o segundo nome\n");
    scanf("%s9", string2);

    printf("Digite o ultimo digito do RU\n");
    scanf("%d", &i);

    strcpy(string3, string1);
    strcpy(&string3[i], string2);

    printf("%s", string3);
}