程序代码：

#include<stdio.h>
int main()
{
    int i;
    char str[30];
    FILE *fp;
    fp=fopen("d:\\123.txt","r+");
    if(fp==NULL) return 0;
    while(!feof(fp))
    {
        i=0;
        fscanf(fp,"%s",str);
        if(!feof(fp))
        {
            while(str[i]!='\0')
                i++;
            str[i+0]='@';
            str[i+1]='q';
            str[i+2]='q';
            str[i+3]='.';
            str[i+4]='c';
            str[i+5]='o';
            str[i+6]='m';
            str[i+7]='\0';

            printf("%s\n",str);
        }

    }
    fclose(fp);
    return 0;
}