程序代码：

#include<stdio.h>
void main()
{
    FILE*f;
    char p[100];
    int n;
    printf("Input a string:\n");
    scanf("%s",&p);
    for(n=0;p[n]!='#';n++)
    {
        if(p[n]<='z'&&p[n]>='a')
            p[n]=p[n]-32;

    }
    p[n]='\0';
    f=fopen("string.txt","w+");
    fprintf(f,"%s",p);
    fclose(f);
}