box-o-sand/digressions/temperatures.c

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#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;
}