append mode

/*  TAHMID RAHMAN
    DAMIAN FOREVER
     MATH LOVER
    NEVER GIVE UP
*/
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int main(int argc, char *argv[])
{
    FILE *fp;
    char str[255];
    int c;

    if(argc!=2)
    {
        printf("Specify file name.\n");
        exit(1);
    }

    while(100)
    {
        printf("Which mode?\n1. Write to file\n2. Read from file\n3. Append to file\n");
        printf("Enter choice:");
        scanf("%d", &c);

        if(c==1)
        {
            if((fp=fopen(argv[1], "w"))==NULL)
            {
                printf("The file does not exist!\n");
                exit(1);
            }

            while(*str!='\n')
            {
                fflush(stdin);
                printf(":");
                gets(str);
                strcat(str, "\n");
                if(*str!='\n')
                    fputs(str, fp);
            }
            fclose(fp);
        }
        if(c==2)
        {
            if((fp=fopen(argv[1], "r"))==NULL)
            {
                printf("The file does not exist.\n");
                exit(1);
            }

            while(!feof(fp))
            {
                fgets(str, 254, fp);
                if(!feof(fp))
                    printf(str);
            }
            fclose(fp);
        }
        if(c==3)
        {
            if((fp=fopen(argv[1], "a"))==NULL)
            {
                printf("The file does not exist!\n");
                exit(1);
            }

            while(*str!='\n')
            {
                fflush(stdin);
                printf(":");
                gets(str);
                strcat(str, "\n");
                if(*str!='\n')
                    fputs(str, fp);
            }
            fclose(fp);
        }
    }
    return 0;
}