If user inputs “sum(x,y)” how can I get x and y as doubles

Question

I am writing a simple calculator program such that the user is entered into the programs own console environment. Each new line starts with a $. User will enter commands such as '''sum(x,y)''' '''mul(x,y)''' etc. and the program will take x and y as doubles and execute a function ie '''double mul(x, y){return x*y)''' and display the returned value.

I have gotten it to correctly identify the command based on matching the first three characters in the string.

I cant seem to read the numerical values correctly no matter what I do. Any suggestions are greatly appreciated!

The Code below is from main()

    printf("%s", " $    ");
    fgets(input, sizeof(input), stdin);
    sscanf(input,"(%d,%d)",&arg1,&arg2);

    if(strstr(input,"sum")){
        //char *starting_pos = strchr(input,dlm);
        //int position = (starting_pos == NULL ? -1 : (uintptr_t)starting_pos);

        //arg1 = input[position + 1];
        //arg2 = input[position + 3];
        printf("DEBUG: arg1 is %d arg2 is %d\n", arg1,arg2);
        double output = sum(arg1,arg2);
        printf("DEBUG: Output should be: %d\n", output);
        printf("%d\n",output);

    }else if ...

The commented section is the remnants of another way I was trying. If anyone can tell me what the right way to do this is I would be very grateful.

Answer 1

Good job in reading with fgets() and then parsing values with sscanf() . If I understand the question, and you may have multiple operators followed by two doubles in parenthesis, eg SUM(1.1, 2.2) , and you want to separate and save the operator, and the double values, then you can use a format string such as:

#define MAXOP   32
...
    char op[MAXOP];
    ...
    sscanf (input, "%31[^( ] (%lf,%lf)", op, &x, &y)

This will read from input separating everything up to a whitespace or '(' into op and then reading the double values into x and y . By reading the op to a whitespace or '(' , you allow input of sum(1.1, 2.2) or sum (1.1, 2.2) seamlessly.

For example, you could do:

#include <stdio.h>

#define MAXC  1024
#define MAXOP   32

int main (void) {
    
    while (1) {
        char input[MAXC], op[MAXOP];
        double x, y;
        
        fputs ("\nenter OP(x, y): ", stdout);
        fflush (stdout);
        
        if (!fgets (input, MAXC, stdin)) {
            puts ("(user canceled input)");
            return 0;
        }
        if (*input == '\n')
            break;
        
        if (sscanf (input, "%31[^( ] (%lf,%lf)", op, &x, &y) == 3)
            printf (" op: '%s'  x: %.2f  y: %.2f\n", op, x, y);
        else
            fputs ("  error: invalid input.\n", stderr);
    }
}

Example Use/Output

./bin/sumxy

enter OP(x, y): mult(10.1,12.4)
 op: 'mult'  x: 10.10  y: 12.40

enter OP(x, y): mult (8.3, 12.1)
 op: 'mult'  x: 8.30  y: 12.10

enter OP(x, y): sum(1.1, pickles)
  error: invalid input.

enter OP(x, y): sum(1.1, 2.2)
 op: 'sum'  x: 1.10  y: 2.20

enter OP(x, y):

Let me know if you have further question, or if I misunderstood the question.