编辑代码

#include <stdio.h>
int main () {
    int x;
    int sum = 0;
    scanf( "%d", & x );
    if( x == 0 ){
        sum = 2;
        printf ( "%d", sum );
    }
    if( x == 1 ){
        sum = 3;
        printf ( "%d", sum );
    }
    if( x > 1 ){
        sum = 3 ;
    }
    int a = 1;
    if( x > 1 ){
        while ( x > 1 ){
            a *= 2;
            sum += a;
            x-- ;
        }
    }
    printf( "面条数量：%d\n", sum);
    
    //JSRUN引擎2.0，支持多达30种语言在线运行，全仿真在线交互输入输出。 
    printf("Hello world!     - c.jsrun.net.");
    return 0;
}