#include <stdio.h>
void Op(n);
int main ()
{
    int n,flag=1;
    char x;
    do{
        printf("----------1:加法运算-----------\n----------2:减法运算-----------\n----------3:乘法运算-----------\n----------4:除法运算-----------\n");
        printf("输入一个数字:");
        scanf("%d",&n);
        Op(n);
        printf("继续-Y/y  退出-N/n");
        scanf("%c",&x);
        if(x=='N' || x=='n')
            flag=0;
    }while (flag==1);
    return 0;

}
void Op(n)
{
    float a,b;
    char x;
    switch(n)
    {
        case 1:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f+%f=%7.2f\n",a,b,a+b);
                break;
            }
        case 2:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f-%f=%7.2f\n",a,b,a-b);   
                break;
            }
        case 3:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f*%f=%7.2f\n",a,b,a*b);
                break;
            }
        case 4:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f/%f=%7.2f\n",a,b,a/b);
                break;
            }
    }
        
}

[ 本帖最后由 龙叩首 于 2013-12-8 16:43 编辑 ]

当你定义时没给n参数类型，我试了一下，第二行和第二十行在n前加int就好了

第四行不是定义了么？

这个不是死循环吗？

int main ()
{
    int n,flag=1;
    char x;
    do{
        printf("----------1:加法运算-----------\n----------2:减法运算-----------\n----------3:乘法运算-----------\n----------4:除法运算-----------\n");
        printf("输入一个数字:");
        scanf("%d",&n);
        Op(n);
        printf("继续-Y/y  退出-N/n");
    fflush(stdin);  //加一句这个（或者getchar();）就OK了  清空缓冲区，否则回车键会键入字符x
        scanf("%c",&x);
        if(x=='N' || x=='n')
            flag=0;
    }while (flag==1);
    return 0;

}

//我帮你执行过，没大问题，有个小问题，向下看
#include <stdio.h>
void Op(int n);//这里  需要这样改
int main ()
{
    int n,flag=1;
    char x;
    do{
        printf("----------1:加法运算-----------\n----------2:减法运算-----------\n----------3:乘法运算-----------\n----------4:除法运算-----------\n");
        printf("输入一个数字:");
        scanf("%d",&n);
        Op(n);
        printf("继续-Y/y  退出-N/n");
        scanf("%c",&x);
        if(x=='N' || x=='n')
            flag=0;
    }while (flag==1);
    return 0;

}
void Op(int n)//同样这里也是这样改。void Op(n),这样是错的
{
    float a,b;
    switch(n)
    {
        case 1:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f+%f=%7.2f\n",a,b,a+b);
                break;
            }
        case 2:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f-%f=%7.2f\n",a,b,a-b);   
                break;
            }
        case 3:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f*%f=%7.2f\n",a,b,a*b);
                break;
            }
        case 4:
            {
                printf("Input 2 number:");
                scanf("%f%f",&a,&b);
                printf("%f/%f=%7.2f\n",a,b,a/b);
                break;
            }
    }
        
}