c - 如何让我的脚本循环并根据命令退出？

Question

我有一个基本脚本，但我不知道如何让它循环并选择通过关键字“退出”结束脚本。

 #include<stdio.h>
 #include<math.h>
 #include<string.h>

 int gcd(int a, int b) {
    while(0!=b) { int r = a % b; a=b; b=r; }
    return a;
}
 int input(char* prompt) {
    int res;
    printf("%s: ", prompt);
    scanf("%d", &res);
    return res;
}
 main()
 {
    int add,sub,mul,dd;
    int add1,sub1,mul1,dd1;
    int a,b,c,d;
    a=input("Please enter the numerator for your first equation");
    b=input("Please enter the denominator for your first equation");
    c=input("Please enter the numerator for your second equation");
    d=input("Please enter the denominator for your second equation");
    add=(a*d+b*c);
    add1=(b*d);
    int fac = gcd(add, add1);
        add /=fac;
        add1 /=fac;
    printf("\The sum of your fractions is: %d/%d",add,add1);
    sub=(a*d-b*c);
    sub1=(b*d);
    int red = gcd(sub, sub1);
        sub /=red;
        sub1 /=red;
    printf("\nThe difference of your fractions is: %d/%d",sub,sub1);
    mul=(a*c);
    mul1=(b*d);
    int red1 = gcd(mul, mul1);
        mul /=red1;
        mul1 /=red1;
    printf("\nThe product of your fractions is: %d/%d",mul,mul1);
    dd=(a*d);
    dd1=(b*c);
    int red2 = gcd(dd, dd1);
        dd /=red2;
        dd1 /=red2;
    printf("\nThe quotient of your fractions is: %d/%d",dd,dd1);
 }

这个想法是让用户能够持续尝试该功能，即使在给出一组结果之后也是如此。话虽如此，用户应该能够在第一个分子问题中输入“quit”，脚本就会结束。有人可以帮我解决这个问题吗？

更新4:

#include<stdio.h>
#include<math.h>
#include<string.h>
#define LINE_SIZE 100
int gcd(int a, int b) {
    while(0!=b) { int r = a % b; a=b; b=r; }
    return a;
}
int input(char* prompt) {
    int res;
   char line[LINE_SIZE];

   printf("%s: ", prompt);
   if ( fgets(line, LINE_SIZE, stdin) == NULL )
   {

      exit(0);
   }

   if (strncmp(line, "quit", 4) == 0 )
   {
      exit(0);
   }

   if ( sscanf(line, "%d", &res) != 1 )
   {
   }

   return res;
}
void computeAndPrint()
{
main();
{
    int add,sub,mul,dd;
    int add1,sub1,mul1,dd1;
    int a,b,c,d;
    a=input("Please enter the numerator for your first equation");
    b=input("Please enter the denominator for your first equation");
    c=input("Please enter the numerator for your second equation");
    d=input("Please enter the denominator for your second equation");
    add=(a*d+b*c);
    add1=(b*d);
    int fac = gcd(add, add1);
        add /=fac;
        add1 /=fac;
    printf("\The sum of your fractions is: %d/%d",add,add1);
    sub=(a*d-b*c);
    sub1=(b*d);
    int red = gcd(sub, sub1);
        sub /=red;
        sub1 /=red;
    printf("\nThe difference of your fractions is: %d/%d",sub,sub1);
    mul=(a*c);
    mul1=(b*d);
    int red1 = gcd(mul, mul1);
        mul /=red1;
        mul1 /=red1;
    printf("\nThe product of your fractions is: %d/%d",mul,mul1);
    dd=(a*d);
    dd1=(b*c);
    int red2 = gcd(dd, dd1);
        dd /=red2;
        dd1 /=red2;
    printf("\nThe quotient of your fractions is: %d/%d",dd,dd1);
 printf("\n");
}

int main();
{
   while ( 1 )
   {
      computeAndPrint();
   }
   return 0;
}

Answer 1

当您可以选择输入数字或字符串quit时，最好使用fgets，后跟strcmp和 sscanf。

// Make LINE_SIZE as large as you need to
#define LINE_SIZE 100

int input(char* prompt) {
   int res;
   char line[LINE_SIZE];

   printf("%s: ", prompt);
   if ( fgets(line, LINE_SIZE, stdin) == NULL )
   {
      // There is no more input
      exit(0);
   }

   if (strncmp(line, "quit", 4) == 0 )
   {
      // The user entered quit
      exit(0);
   }

   // Expect to see a number
   if ( sscanf(line, "%d", &res) != 1 )
   {
      // Deal with the error
   }

   return res;
}

更新，回应OP的评论

1. 将 main 的核心移至辅助函数。
2. 在main中使用while循环。在 while 循环中，调用辅助函数。

void computeAndPrint()
{
   int add,sub,mul,dd;
   int add1,sub1,mul1,dd1;
   int a,b,c,d;

   printf("\n");
   a=input("Please enter the numerator for your first equation");
   b=input("Please enter the denominator for your first equation");
   c=input("Please enter the numerator for your second equation");
   d=input("Please enter the denominator for your second equation");

   add=(a*d+b*c);
   add1=(b*d);
   int fac = gcd(add, add1);
   add /=fac;
   add1 /=fac;
   printf("\nThe sum of your fractions is: %d/%d",add,add1);

   sub=(a*d-b*c);
   sub1=(b*d);
   int red = gcd(sub, sub1);
   sub /=red;
   sub1 /=red;
   printf("\nThe difference of your fractions is: %d/%d",sub,sub1);

   mul=(a*c);
   mul1=(b*d);
   int red1 = gcd(mul, mul1);
   mul /=red1;
   mul1 /=red1;
   printf("\nThe product of your fractions is: %d/%d",mul,mul1);

   dd=(a*d);
   dd1=(b*c);
   int red2 = gcd(dd, dd1);
   dd /=red2;
   dd1 /=red2;
   printf("\nThe quotient of your fractions is: %d/%d",dd,dd1);

   printf("\n");
}

int main()
{
   while ( 1 )
   {
      computeAndPrint();
   }
   return 0;
}