I started studying my first language ‘C’ and I’m trying to solve a linear system. But I’m having trouble putting together a function that equates the terms on the left side with the right side of the equality.
When entering the equation (example: N2 + H2 = NH3): N2 + H2 = NH3
I obtain its elements and its unknowns from the equation:
N2 = 2a
H2 = 2b
NH3 = 3c
and with the function below I expected
2a = c
2b = 3c
But I only get 2a = 3a

// Function to equalize the unknowns on the right side with the left side of the equation
void equalize_unknowns(char equation[]) {
    int i, len;
    char left_side[MAX_LEN];
    char right_side[MAX_LEN];
    char unknown = 'a'; // Initial unknown

    // Divide the equation into left and right sides
    sscanf(equation, "%[^=]=%s", left_side, right_side);
     printf("nSetting up the system:n");

    // Iterate over the left and right sides to equalize the unknowns
    char *token_left = strtok(left_side, "+");
    char *token_right = strtok(right_side, "+");

    while (token_left != NULL && token_right != NULL) {
        char element_left[MAX_LEN];
        char element_right[MAX_LEN];
        int coef_left, coef_right;

        sscanf(token_left, "%[^0-9]%d", element_left, &coef_left);
        sscanf(token_right, "%[^0-9]%d", element_right, &coef_right);

        printf("%d%c = %d%cn", coef_left, unknown, coef_right, unknown);

        token_left = strtok(NULL, "+");
        token_right = strtok(NULL, "+");
    }
}

Code without the function that assembles the linear system

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

#define MAX_LEN 100

// Function to check if a character is a digit
int is_digit(char c) {
    return (c >= '0' && c <= '9');
}

// Function to process the equation and print the elements with their unknowns
void process_equation(char equation[]) {
    int i, len;
    int coefficient = 1; // Initialize coefficient as 1 (if none is specified)
    char element[MAX_LEN];
    char unknown = 'a'; // Initial unknown

    printf("Elements and their unknowns in the equation:n");
    for (i = 0; i < strlen(equation); i++) {
        if (isalpha(equation[i])) { // If it's a letter (element)
            int j = 0;
            while (isalpha(equation[i])) {
                 element[j++] = equation[i++];
            }
            element[j] = '';

            // Check if the next character is a number (coefficient)
            if (is_digit(equation[i])) {
                coefficient = 0;
                while (is_digit(equation[i])) {
                    coefficient = coefficient * 10 + (equation[i++] - '0');
                }
            }

            // Print the element with its associated unknown
            printf("%s%d = %d%cn", element, coefficient, coefficient, unknown++);
            coefficient = 1; // Reset coefficient for the next term
        }
    }
}

// Function to equalize the unknowns on the right side with the left side of the equation
int main() {
    char equation[MAX_LEN];

    printf("Enter the chemical equation (example: N2 + H2 = NH3): ");
    fgets(equation, MAX_LEN, stdin);

    // Remove the 'n' added by fgets
    equation[strcspn(equation, "n")] = '';

    // Process the equation and print the elements with their unknowns
    process_equation(equation);

    // Equalize the unknowns on the right side with the left side of the equation

    return 0;
}