Squaring a number

Question

This program is supposed to input a number and its square value, then tell me if right or wrong. I have some problems but I can't figure out what they are.

#include <stdio.h>
#include <math.h>
int main()
{
    float P;
    float q;
    float r;
    printf("Enter the value of p\n");
    scanf("%f",p);
    q= p*p;
    printf("Enter the square value of %f \n",p);
    scanf("%f",r);
    if (r = q){
        printf("You are right\n");
    }
    else{
        printf("you are wrong\n");
    }
    return 0;
}

so tell me my mistakes

Your code is essentially unreadable, bu this 'scanf("%f",p);' cannot possibly modify 'p' since it is passsed by value. — Martin James, Apr 16 '16 at 19:28
Your first mistake was not learning how to run your program under a debugger. — Martin James, Apr 16 '16 at 19:31
@MartinJames I don't agree, it's the second error. First error is not using good compiler flags. — jdarthenay, Apr 16 '16 at 19:36
@jdarthenay there are good compiler flags? .. Oh never mind :) — Martin James, Apr 16 '16 at 19:40
@MartinJames At least some compiler settings such as no flags at all are worst than others, that's for sure. — jdarthenay, Apr 16 '16 at 19:42
@WeatherVane Definitely not, OP does not even reach that point... — jdarthenay, Apr 16 '16 at 19:48

score 2 · Answer 1 · edited May 23 '17 at 12:31

2

Please compile the program with flags -Werror -Wall -Wextra although the first mistake is always a compilation error (typo): replace float P; with float p; because C is case-sensitive.

Then you need to pass the address of a variable to scanf, these two lines

scanf("%f",r);
...
scanf("%f",p);

should be

scanf("%f",&r);
...
scanf("%f",&p);

Lastly, there is a syntax error where you test for equality with

if (r = q)

but this changes r and tests if it is non-0. With an integer type you should use

if (r == q)

but with floating point types, equality tests don't work well, please see why in this question.

edited May 23 '17 at 12:31

Community

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answered Apr 16 '16 at 19:29

jdarthenay

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@WeatherVane That's already said in my answer... – jdarthenay Apr 16 '16 at 19:43
@WeatherVane Well, I didn't have the feeling I was doing that, I'll try to turn my answer differently. – jdarthenay Apr 16 '16 at 19:45
@WeatherVane I would upvote your edit if I could... – jdarthenay Apr 16 '16 at 20:16
I upvoted your answer, it was good, I just improved the phrasing. – Weather Vane Apr 16 '16 at 20:17

Squaring a number

1 Answers1