How can I perfectly truncate a string in c?

**I try to truncate this string but it always gives me this answer:

**"-bash-3.00$ a.out String: xxxxxxxxxxooooooooooÿ>Á¬ÿ>ð¬"

//**Please what should I do? Thanks.

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

int main(void)
{

    char a[10][63];

    char line[50] = "xxxxxxxxxxooooooooooaaaaaaaaaakkkkkkkkkkkk";

    //Tries to truncate "line" to 20 characters
    line[20] = '\0';

    //copying line to each character at a time
    int x;
    for(x = 0; x < 20; x++)
    {
        a[0][x] = line[x];
    }

    //Printing out the copied character.
    printf("String: %s\n", a[0]);
}