就是else的前面少了一个右大括号},,
if (lower<=upper){这一段结束后面少了一个相匹配的大括号},修改如下:
#include <stdio.h>
int main(void){
int lower,upper,fahr;
double celsius;
scanf("%d %d",&lower,&upper);
if(lower<=upper){
printf("fahr celsius\n");
for(fahr=lower;fahr<=upper;fahr=fahr+2){
celsius = 5.0*(fahr-32)/9.0;
printf("%d%6.1lf\n",fahr,celsius);
}
}else{
printf("Invalid");
}
return 0;
}