???

main.c

/* ??? */
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

int main(int argc, char *argv[])
{
        // two arguments required one string input and one the number of '?' to be added
        if(argc != 3)
        {
                printf("not enough arguments %s <string> <number '?'>\r\n", argv[0]);
                return 1;
        }

        int numbersymbols = atoi(argv[2]);
        char bufferstr[1024];

        // carefull strlen returns the number of characters does not include the zero terminator.
        memcpy(bufferstr, argv[1], strlen(argv[1]) + 1);
        printf("bufferstr: %s\r\n", bufferstr);

        int i = 0;
        for(i = 0; i < numbersymbols; i++)
        {
                bufferstr[strlen(argv[1]) + i] = '?';
                bufferstr[strlen(argv[1]) + i + 1] = '\0'; // always end with a zero terminator!
        }

        printf("strlen(\"%s\") = %ld \r\n", argv[1], strlen(argv[1]));
        printf("result: %s\r\n", bufferstr);
}