程序代码：

#include<stdio.h>
#include<stdlib.h>
int main()
{

    char c;
    char filename[80];
    char temp[1000];
    FILE *fp;
    printf("Please input file path:");
    gets(filename);
    if((fp=fopen(filename,"r+"))==NULL)
    {
        printf("file %s can't opened \n",filename);
        exit(0);
    }
    int i=0;
    while((c=fgetc(fp))!=EOF)
    {
        //c='a'<=c&&c<='z'?c-'a'+'A':c;
        if((c>='a')&&(c<='z'))
            c=c-'a'+'A';
        temp[i]=c;
        i++;
        //fputc(c,fp);
    }
    fclose(fp);
    fp=fopen(filename,"w+");
    int j=0;
    while(j<i)
    {
        c=temp[j];
        j++;
        fputc(c,fp);
    }
    fclose(fp);
}

程序代码：

#include"stdio.h"
main()
{
    int c;
    char filename[80];
    long offset;
    FILE *fp;

    printf("Please input file path:");
    gets(filename);
    if((fp=fopen(filename,"r+"))==NULL)
    {
            printf("file %s can't opened \n",filename);
            exit(0);
    }
    while((c=fgetc(fp))!=EOF)
    {
            c=('a'<=c&&c<='z'?c-'a'+'A':c);
            /*printf("%c",c);*/
            offset=ftell(fp);
            fseek(fp,offset-1,SEEK_SET);
            fputc(c,fp);
            offset=ftell(fp);
            fseek(fp,offset,SEEK_SET);
    }
    fclose(fp);
}