C Program - Double returns zero

Question

This is the C program

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

int main (void){

    double voltage, resistance;
    printf("Enter your Voltage: ");
    scanf("%f", &voltage);
    printf("Enter your Resistance: ");
    scanf("%f", &resistance);
    double amps = voltage / resistance;
    printf("With voltage %f and Ohm %fohms, amps is equal to %f \n", voltage, resistance, amps);
    return 0;
}

Why is voltage and resistance variables returning values of 0.00?

Hey thanks that worked, can you please explain what adding the 'l' does? — Vbobo, Mar 20 '16 at 09:25
You might like to RTFM on `scanf()`: http://www.iso-9899.info/n1570.html#6.2.5p28 — alk, Mar 20 '16 at 09:26
Your compiler should have warned on the mismatch between format-specifier and the type of argument passed. If not increase its warning level. Take warnings serious. — alk, Mar 20 '16 at 09:29
OT: Your result string is missing units for voltage and current, as well as the input prompts do. The unit for resistance is not "ohms" but "Ohm", short Ω. — alk, Mar 20 '16 at 09:31

Some programmer dude · Answer 1 · 2021-12-13T06:57:03.333

5

For scanf (and family) the format "%f" is for float, to get a double you need a "long" float which have the format-prefix l as in "%lf".

It should be noted that for printing floating point values with printf, all float arguments will be promoted to double. Which means that for printf there's no difference between %f and %lf.

edited Dec 13 '21 at 06:57

answered Mar 20 '16 at 09:26

Some programmer dude

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score 2 · Answer 2 · answered Mar 20 '16 at 09:24

You should use %lf in your scanf.

This worked nice for me:

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

int main (void){

double voltage, resistance;
printf("Enter your Voltage: ");
scanf("%lf", &voltage);
printf("Enter your Resistance: ");
scanf("%lf", &resistance);
double amps = voltage / resistance;
printf("With voltage %f and Ohm %fohms, amps is equal to %f \n", voltage, resistance, amps);
return 0;
}

C Program - Double returns zero

2 Answers2