#include<stdio.h>

#include<stdlib.h>
#include<string.h>
#define LEN 40

int main(int argc,char *argv[])
{
    FILE *in,*out;
    int ch;
    char name[LEN];
    int count=0;

    if(argc<2)
    {   
        fprintf(stderr,"Usage: %s filename\n",argv[0]);
        exit(1);
    }

    if((in=fopen(argv[1],"r"))==NULL)
    {
        fprintf(stderr,"I couldn't open the file \"%s\"\n",
            argv[1]);
        exit(2);


    }
    strcpy(name,argv[1]);
    strcat(name,".red");
    if((out=fopen(name,"w"))==NULL)
    {
        fprintf(stderr,"Can't creat puput file.\n");
        exit(3);

    }

    while((ch=getc(in))!=EOF)
        if(count++%3==0)
            putc(ch,out);

    if(fclose(in)!=0||fclose(out)!=0)
        fprintf(stderr,"Error in closing files.\n");

    return 0;


}

代码如上，生成.exe为peoject8.exe  用命令行操作时，我把peoject8.exe复制到了lenovo文件夹下，并创建了tet.txt文件，
运行后提示I couldn't open the file "tet"

因为是刚接触文件操作，所以不知道哪里错了，希望大家可以指导下

运行的时候要带参数，比如peoject8 tet.txt

额，谢谢