如何让我的脚本循环并退出命令？

Question

我有一个基本的脚本，但我无法弄清楚如何让它通过一个关键词“退出”结束脚本的选项循环。

#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连续尝试功能，即使在给出一组结果后。据说，用户应该能够在第一个分子问题中键入“quit”，脚本将结束。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

当你输入号码或串quit的选项，最好使用之后strcmp和sscanffgets。

// 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，响应OP的评论

1. 移动的main核心，以辅助函数。
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; 
}