#include<iostream>
using  namespace std ;
int main()
{
    int first_num;
    int second_num;
    int sign;
    cout<<"enter the first_number:"<<'\n';
    cin>> first_num;
    cout<<"enter the second_number:"<<'\n';
    cin>>second_num;
    cout<<"enter the arithmetic sign :"<<'\n';
    cin>>sign;
    if ( sign== + )
    {
        cout<<first_num<<"+"<<second_num<<"="<<first_num + second_num<<endl;
    }
    else if(sign==-)
    {
        cout<<first_num<<"-"<<second_num<<"="<<first_num - second_num<<endl;
    }
    else if(sign==*)
    {
        cout<<first_num<<"*"<<second_num<<"="<<first_num * second_num<<endl;
    }
   else(sign==/);
    {
        cout<<first_num<<"/"<<second_num<<"="<<first_num / second_num<<endl;
        return 0;
    }
}
报错是：
||=== Build: Debug in 入门练习 (compiler: GNU GCC Compiler) ===|
D:\软件\C++\C++文件\入门练习\main.cpp||In function 'int main()':|
D:\软件\C++\C++文件\入门练习\main.cpp|14|error: expected primary-expression before ')' token|
D:\软件\C++\C++文件\入门练习\main.cpp|18|error: expected primary-expression before ')' token|
D:\软件\C++\C++文件\入门练习\main.cpp|22|error: expected primary-expression before ')' token|
D:\软件\C++\C++文件\入门练习\main.cpp|26|error: expected primary-expression before '/' token|
D:\软件\C++\C++文件\入门练习\main.cpp|26|error: expected primary-expression before ')' token|
||=== Build failed: 5 error(s), 0 warning(s) (0 minute(s), 0 second(s)) ===|

没有弄明白为什么那个地方有错*_*

还有有时候莫名其妙的会报错else if前面应该先用if，可是我用过if了呀。。。网上有人说可能是没有大括号，我加了还是不行T_T
就是有时候好好的有时候会报错，但找不到错跟没错有什么不一样的地方

a,数据类型有问题
b,if语句后面加分号，楼主这是在作死的节奏哎
#include<iostream>
using  namespace std ;
int main()
{
    int first_num;
    int second_num;
    char sign;
    cout<<"enter the first_number:\n";
    cin>> first_num;
    cout<<"enter the second_number:\n";
    cin>>second_num;
    cout<<"enter the arithmetic sign :\n";
    cin >> sign;
    if ( sign == '+' )
    {
        cout<<first_num<<"+"<<second_num<<"="<<first_num + second_num<<endl;
    }
    else if(sign =='-')
    {
        cout<<first_num<<"-"<<second_num<<"="<<first_num - second_num<<endl;
    }
    else if(sign=='*')
    {
        cout<<first_num<<"*"<<second_num<<"="<<first_num * second_num<<endl;
    }
   else if(sign=='/')
    {
        cout<<first_num<<"/"<<second_num<<"="<<first_num / second_num<<endl;      
    }
    return 0;
}


[ 本帖最后由 hjx1120 于 2015-7-23 22:30 编辑 ]

int first_num;
    int second_num;
    char sign;
    printf("enter the first_number:\n");
    scanf("%d", &first_num);
    printf("enter the second_number:\n");
    scanf("%d", &second_num);
    printf("enter the arithmetic sign :\n");
    scanf(" %c", &sign);
   
   
    if ( sign == '+' )
    {
        printf("%d + %d = %d\n", first_num, second_num, first_num + second_num);
      
    }
    else if(sign =='-')
    {
        printf("%d - %d = %d\n", first_num, second_num, first_num - second_num);
    }
    else if(sign=='*')
    {
        printf("%d * %d = %d\n", first_num, second_num, first_num * second_num);
    }
    else if(sign=='/')
    {
        printf("%d / %d = %d\n", first_num, second_num, first_num / second_num);
    }

问题解决啦....
蟹蟹*_*