about "argc and argv"

[8279 0] % cat foo.c

#include 

int main(int argc, char *argv[])
{
    int i;

    printf("argc = %d\n", argc);
    for (i = 0; argv[i]; i++) {
        printf("argv[%d] = '%s'\n", i, argv[i]);
    }

    return 0;
}

[8279 0] % gcc foo.c
[8279 0] % ./a.out
argc = 1
argv[0] = './a.out'
[8279 0] % ./a.out 1 2 3
argc = 4
argv[0] = './a.out'
argv[1] = '1'
argv[2] = '2'
argv[3] = '3'
[8279 0] % ./a.out hello world
argc = 3
argv[0] = './a.out'
argv[1] = 'hello'
argv[2] = 'world'