C言語は簡単な計算機(プラス、マイナス、乗数、除算、型取り)を作る

#include

int main()
{
    double number1=0.0;
    double number2=0.0;
    char operation=0;

    a:
    printf("         （  a+b）：
");
    scanf("%lf%c%lf",&number1,&operation,&number2);

    if(operation=='+')
    {
        printf("      ，     ：%lf
",number1+number2);
    }
    else if(operation=='-')
    {
        printf("      ，     ：%lf
",number1-number2);
    }
    else if(operation=='*')
    {
        printf("      ，     ：%lf
",number1*number2);
    }
    else if(operation=='/')
    {
        if(number2==0)
        {
            printf("           :
");
            goto a;
        }
        else
        {
            printf("      ，     ：%lf
",number1/number2);
        }
    }
    else if(operation=='%')
    {
        if(number2==0)
        {
            printf("           :
");
            goto a;
        }
        else
        {
            printf("      ，     ：%ld
",(long)number1%(long)number2);
        }
    }
    else
    {
        printf("      ，     ！");
    }

    return 0;
}