#include <stdio.h>

int main(void)
{
  int choice = 0;
  double temperature = 0.0;
  printf("This program can do the following:\n"
         "1. Convert from degrees Centigrade to degrees Fahrenheit\n"
         "2. Convert from degrees Fahrenheit to degrees Centigrade\n"
         "Select the conversion (1 or 2): ");
  scanf("%d", &choice);

  printf("Enter a temperature in degrees %s: ",//这句是不是多余的//
                          (choice == 1 ?  "Centigrade" : "Fahrenheit"));//为什么要用这个表达式，难道不和下面的if重复吗//
  scanf("%lf", &temperature);
  if(choice == 1)
    printf("That is equivalent to %.2lf degrees Fahrenheit\n", temperature*9.0/5.0+32.0);
  else
    printf("That is equivalent to %.2lf degrees Centigrade\n", (temperature-32.0)*5.0/9.0);
  return 0;
}

我觉得不重复     printf("Enter a temperature in degrees %s: ",(choice == 1 ?  "Centigrade" : "Fahrenheit"));的作用只是输出
Enter a temperature in degrees Centigrade或
Enter a temperature in degrees  Fahrenheit。
我觉得这样做更能给别人起到提示的作用
IF里的是处理

(choice == 1 ?  "Centigrade" : "Fahrenheit")这个是什么意思

choice是不是等于1   是打印Centigrade    不是就打印Fahrenheit

不重复啊，

如果你觉得重复的话，printf语句放在if语句后面