>>30
#include <stdio.h>
#include <string.h>
int main( void )
{
double a, b;
char c;
char* ptr = " +-*/";
int t;

while( 1 ) {
printf( "0:無指定 1:加算 2:減算 3:乗算 4:除算 5:終了-> " ); scanf( "%d", &t );
if( t == 5 ) break;
printf( "式入れれ\n" ); scanf( "%lf%c%lf", &a, &c, &b );
if( ! t )t = strchr( ptr, c ) - ptr;
if( t < 1 && t > 4 || ptr[t] != c ) {
printf( "却下\n" );
continue;
}
switch( t ) {
case 1: printf( "%lf + %lf = %lf\n", a, b, a + b ); break;
case 2: printf( "%lf - %lf = %lf\n", a, b, a - b ); break;
case 3: printf( "%lf * %lf = %lf\n", a, b, a * b ); break;
default: printf( "%lf / %lf = %lf\n", a, b, a / b ); break;
}
}
return 0;
}