[求助]如何在程序中添加命令行变元

如何在程序中添加命令行变元，如同这条程序，怎样才能使argc==3，来运行全部功能呢？
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
#include<string.h>
int main(int argc,char *argv[])
{
int disp,count;
if(argc<2){
printf("You must enter the length of the count\n");
printf("on the commamd line,Try again.\n");
exit(1);
}
if(argc==3&&!strcmp(argv[2],"display")) disp=1;
else disp=0;
for(count=atoi(argv[1]);count;--count)
if(disp) printf("%d\n",count);
putchar('\a');
printf("Done");
return 0;
}