Reading fractions in C

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臣服心动 2021-01-14 23:45

How do I read a fraction into C to do math with it? (The fraction will contain the slash symbol) For example, A user will input 3/12. (a string) The program will find the gc

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  • 2021-01-15 00:29

    Keep a pointer to the head of the string.

    Then look into using strchr() to get a second pointer that points to the / character.

    You can then:

    1. Read characters from a dereferenced first pointer up until your first pointer is equal to the second pointer. Store those characters into a char [] or char * — that's your numerator as a C string.
    2. Read from the next character after where the second pointer points, up to the /0 nul terminator at the end of the string. Store those characters in a second char [] or char * — that's your denominator as a C string.

    Use atoi() to convert both C strings to integers.

    If strchr() returns NULL, then you can do error checking very easily because there was no / in the input string.

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  • 2021-01-15 00:35

    This uses sscanf to get the numbers, you can use scanf directly of course:

    #include <stdio.h>
    int main() {
      const char *s = " 13/6  \n";
      int a,b;
      sscanf(s, "%d/%d", &a, &b);
      printf("%d frac %d\n", a, b);
      return 0;
    }
    
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  • 2021-01-15 00:36
    #include <stdio.h>
    
    typedef struct
    {
    int num, denom;
    }fraction;
    
    int main()
    {
    fraction fract = {1,2};
    
    printf("fraction: %i/%i", fract.num, fract.denom);
    return 0;
    }
    
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  • 2021-01-15 00:40

    Alright. I've got a different way. Use strtol which will return to you a pointer to the '/' to which you add 1 and call strtol again for the second half.

    This is twice as fiddly as the first answer, halfway as fiddly as the second. :)

    #include <stdio.h>
    #include <string.h>
    
    int main(){
        char *f = " 12/7 ";
        char *s;
        long n,d;
        n = strtol(f, &s, 10);
        d = strtol(s+1, NULL, 10);
        printf(" %ld/%ld \n", n, d);
        return 0;
    }
    

    To answer the rest of your question, you definitely need 2 variables if it's going to be a fraction. If you can use floating-point internally and the fractions are just a nice feature for user input, then you can go ahead and divide them and store the number in one variable.

    double v;
    v = (double)n / d;
    

    The cast to double is there to force a floating-point divide upon the two integers.

    If, on the other hand you're going to have a lot of fractions to work with, you may want to make a structure to hold them (an object, if you will).

    struct frac {
        long num;
        long den;
    };
    struct frac f = { 12, 7 };
    printf("%ld/%ld\n", f.num, f.den);
    
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  • 2021-01-15 00:49

    you can make it this way also......

      char str[30];
      scanf("%s",str);
      char c[30];
      int i, num, denom;
    
      i = 0;
      while (*(str+i) != '/')
      {
          memcpy((c+i), (str+i), 1);
          i++;
      }
      *(c+i) = 0;
      i++;
      num = atoi(c);
      strcpy(c, (str+i));
      denom = atoi(c);
      printf("%d\n", num);
      printf("%d\n", denom);
    
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  • 2021-01-15 00:49

    Here's what I generally do.

    int main()
    {
    double a,b=1.0f,s;
    scanf("%lf/%lf",a,b);
    s=a/b;
    printf("%lf",s);
    }
    

    Even if the user the doesn't enter the value of variable b the value is already initialized to 1.0f so it can calculate it's value anyway.

    This is tried on Ubuntu with GCC.

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