Pull 10/3 from string and perform the math in C - c

Question

Could anyone help me figure out how to extract 10/3 from a string, perform the math of 10/3 as a float/double, and store the result? I've tried modifying an older code that I have but I couldn't get it to work. This is that code:
#include<stdio.h>
#include<string.h>
#define SLASH "\\."
int main(void){
char path[100];
printf("Enter file path: \n");
fgets(path, sizeof(path), stdin);
path[strlen(path) - 1] = '\0';
char *token = strtok(path, SLASH);
while(token != NULL){
printf("%s\n", token);
/*Rather than printf the result
I've tried saving the result to
a variable but I could only get
10 to save*/
token = strtok(NULL, SLASH);
}
return 0;
}
I will then be putting the solution into this portion of a larger program:
} else if(j == 6){
arr3[j][(strlen(arr3[j])) - 1] = NULL;
sprintf(temp_arr, "%.18lf", atof(arr3[j]));
strcat(arr3[j], temp_arr);
strcat(arr3[j], new_line);
} else if(j == 7){
I read the following in from a .csv file:
input from file:
The output that I need to obtain is:
Correct output:
Could anyone give me some ideas on how to do this? I've tried to do a for loop instead of a while loop in hopes to save 10 to an array[0] and 3 to an array[1 ], but I would only get array[0] = 10 and array[1 ] = 0. Other times I would just get random junk instead of zero. Using this token approach seemed so straight-forward before but I can't convert for this task. It doesn't seem like this should be so hard for me but I'm stuck. Thanks in advance for any help that anyone can provide.
Edit:
I tweaked the first code to save each separately:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#define SLASH "\\."
int main(void){
char path[100];
printf("Enter file path: \n");
fgets(path, sizeof(path), stdin);
path[strlen(path) - 1] = '\0';
char *token = strtok(path, SLASH);
while(token != NULL){
int i = 0;
char temp[100];
strcpy(temp, token);
printf("%s\n", token);
printf("temp = %s\n", temp);
token = strtok(NULL, SLASH);
i++;
}
return 0;
}
From there, I'm trying to implement that into the program that I'm actually working on.
char temp_arr[17];
} else if(j == 6){
arr3[j][(strlen(arr3[j])) - 1] = '\0';
strcpy(temp_arr, arr3[j]);
char *token = strtok(arr3[j], SLASH);
int m = 0;
while(token != NULL){
strcpy(temp_arr2, token);
printf("temp = %s\n", temp_arr2);
token = strtok(NULL, SLASH);
m++;
}
sprintf(temp_arr, "%.18lf", atof(arr3[j]));
strcat(arr3[j], temp_arr);
strcat(arr3[j], new_line);
But I'm getting 10/3 instead of 10 and 3 separately.

Answer 1

There are a number of ways to approach this problem. One of the simplest is to parse the string using the capabilities of strtol which will parse a string for a numeric value, convert the value to a long, and set its endptr parameter to point to one character after the last digit used in the conversion.
(which will be '/' in your case, but you should still check for any intervening spaces between the end of the number and your operator)
You can then start scanning forward from endptr until you locate '/' (or any non-numeric character to use for the operator). Save the character, and advance your pointer by one and call strtol again to convert your final number to long.
Putting the pieces together, you can do something like the following:
#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#define BASE 10
#define EXPR 64
int main (void) {
long a, b;
char op,
expr[EXPR] = "",
*p = expr,
*ep;
printf ("enter expression: ");
if (!fgets (expr, EXPR, stdin)) {
fprintf (stderr, "error: user canceled input.\n");
return 1;
}
a = strtol (p, &ep, BASE); /* convert a to long */
if (p == ep) { /* no digits converted */
fprintf (stderr, "error: strtol - a, no digits found.\n");
return 1;
}
p = ep; /* set p to end-pointer */
while (*p && isspace (*p)) p++; /* skip any intervening spaces */
op = *p++; /* set operator char */
b = strtol (p, &ep, BASE); /* convert b to long */
if (p == ep) { /* no digits converted */
fprintf (stderr, "error: strtol - b, no digits found.\n");
return 1;
}
printf ("%ld %c %ld = ", a, op, b); /* output expression */
switch (op) { /* handle +, -, *, / */
case '+': printf ("%ld\n", a + b); break;
case '-': printf ("%ld\n", a - b); break;
case '*': printf ("%ld\n", a * b); break;
case '/': printf ("%f\n", (double)(a) / b); break;
default : printf ("(error - invalid operator)\n"); break;
}
return 0;
}
(note: you should also check errno following each call to strtol to insure there were no errors, overflow/underflow, etc.. in the conversion. That is left to you)
Example Use/Output
$ ./bin/aexprb
enter expression: 10/3
10 / 3 = 3.333333
$ ./bin/aexprb
enter expression: 10 / 3
10 / 3 = 3.333333
$ ./bin/aexprb
enter expression: 10 + 3
10 + 3 = 13
Look things over and let me know if you have further questions.