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


double c2f(double celsius) {
    return ((9.0 / 5.0) * celsius) + 32.0;
}


double f2c(double fahrenheit) {
    return (5.0 / 9.0) * (fahrenheit - 32.0);
}


int die_usage(const char *msg) {
    printf("Usage: temperatures [FC]<temp>\n");
    printf("%s\n", msg);
    exit(1);
}


int main(int argc, char * argv[]) {
    if (argc < 2) {
        die_usage("");
    }

    char msg[255];
    double temp;
    const char * temp_string = argv[1];

    size_t temp_len = strlen(temp_string);

    if (strncmp(temp_string, "F", temp_len) > -1) {
        sscanf(temp_string, "F%lf", &temp);
        printf("%.2lf\n", f2c(temp));
    } else if (strncmp(temp_string, "C", temp_len) > -1) {
        sscanf(temp_string, "C%lf", &temp);
        printf("%.2lf\n", c2f(temp));
    } else {
        sprintf(msg, "Argument '%s' does not match '[FC]<temp>'",
                temp_string);
        die_usage(msg);
    }

    return 0;
}