# include <stdio.h>
int main()
{
    int n, u, i, m;
    printf("=== This is a Number Guess Game ===\n");
    printf("Please input a Password:\n");scanf("%d",&u);   
    if(u != 765){for(i=3; i>1; )
    {
        --i;printf("This Password is wrong, you just have %d times to input again\n", i);
        scanf("%d",&u);
    }
    return 0;
    }else
    {
    do{printf("please input a number between 1 to 100 !:\n");
    scanf("%d",m);printf("Your input number is %d\n", m);}while(m>=1 && m<=100);
    if(m>=50 && m<60)printf("Sorry,Only a little smaller! Press any key to try again!\n");
    else if(m>60 && m<=70)
        printf("Sorry,Only a little bigger! Press any key to try again!\n");
    else if(m>=40 && m<50)
        printf("Small! Press any key to try again!\n");
    else if(m>70 && m<=80)
        printf("Big! Press any key to try again!\n");
    else if(m>=1 && m<40)
        printf("Too Small! Press any key to try again!\n");
    else if(m>80 && m<=100)
        printf("Too Bigger! Press any key to try again!\n");
    else if(m=60)printf("OK! You are right! Bye Bye!\n");
    }
}

scanf("%d",m);

就凭这一点，你敢说你的程序编译能通过？！

另外，感觉你的这个程序的逻辑有点问题

建议你最好先想清楚这个问题到底是怎么个事儿？

起码你的循环用的就不太对。。