Can't define a variable

Question

The compiler throws an 'unused variable error', when I try to declare any type of variable and assign it a value. Below I use 'float' as the variable type and try and assign it to 1.5.

#include <stdio.h>
#include <cs50.h>

int main(void)
{
    printf("How long is your shower?\n");
    int time = GetInt();

    float flow = 1.5;
}

The compiler throws this error:

~/workspace/pset1/ $ make water
clang -ggdb3 -O0 -std=c11 -Wall -Werror -Wshadow    water.c  -lcs50 -lm -o water
water.c:10:11: error: unused variable 'flow' [-Werror,-Wunused-variable]
    float flow = 1.5;
          ^
1 error generated.
make: *** [water] Error 1

It seems that this issue is already explained here : [enter link description here](http://stackoverflow.com/questions/19750690/wunused-variable-compiler-says-error) — P.Bra, Sep 26 '16 at 07:01
`#include ` isn't part of C, is not shown, nor involved in your issue. You want to remove it from your example code. — alk, Sep 26 '16 at 07:12

score 6 · Answer 1 · answered Sep 26 '16 at 06:58

6

flow isn't used by your program - it is not involved in any side effects, you just assign a value to it and discard it. Good compilers warn against such unused variables.

By using -Werror you turned the warning into an error.

answered Sep 26 '16 at 06:58

Lundin

195,001
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396

Wolph · Accepted Answer · 2016-09-26T07:50:29.110

3

It's actually a warning and not an error but because of the -Werror flag you see it as an error.

Long story short, if you use the variable it won't return the error anymore.

#include <stdio.h>
#include <cs50.h>

int main(void)

{
    printf("How long is your shower?\n");
    int time = GetInt();

    float flow = 1.5;
    printf("Flow: %.2f, time: %d", flow, time);
}

edited Sep 26 '16 at 07:50

answered Sep 26 '16 at 06:57

Wolph

78,177
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but now it will warn about the `time` variable: http://ideone.com/Dzkjix – mch Sep 26 '16 at 07:39
@mch: fair enough, I've added that one to the print statement as well :) – Wolph Sep 26 '16 at 07:50

score 1 · Answer 3 · answered Sep 26 '16 at 06:58

1

Seems legit, you are not using the variable anywhere. Try printing it out;

printf("%.2f", flow);

answered Sep 26 '16 at 06:58

Laazo

467
8
22

Can't define a variable

3 Answers3