manipulate command line

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

int main(int argc, char** argv) {
    for(int i=0; i<argc; i++) {
        printf("%s\n", argv[i]);
        for(int c=0; c<strlen(argv[i]); c++){
            argv[i][c]='x';
        }
    }
    system("sleep 60");
}
peter@peter:~/tmp/changecl.c$ gcc -std=c99 changecl.c
peter@peter:~/tmp/changecl.c$ ./a.out --help &

peter@peter:~/tmp/changecl.c$ echo $!
1359

peter@peter:~/tmp/changecl.c$ ps -ef | grep 1359
peter     1359 19837  0 13:30 pts/19   00:00:00 xxxxxxx xxxxxx
peter     1360  1359  0 13:30 pts/19   00:00:00 sleep 60
peter     1400  1361  0 13:31 pts/20   00:00:00 grep --color=auto 1359

peter@peter:~/tmp/changecl.c$ cat /proc/1359/cmdline
xxxxxxxxxxxxx

peter@peter:~/tmp/changecl.c$ hexdump -C /proc/1359/cmdline
00000000  78 78 78 78 78 78 78 00  78 78 78 78 78 78 00     |xxxxxxx.xxxxxx.|
0000000f