Why do I get a segmentation error here in my code?

Question

It's an extremely simple code, when I run it, it lets me enter the int, but when I enter it, the program crashes. I tried putting a printf right after the scanf to check if the program reads the int correctly, it seems it doesn't. I can't output the integer that I input.

#include <stdio.h>
#include <math.h>

void coolfunction(int x, int *y)
{
    *y = exp(x);
}

int main()
{
    int n;
    double result = 0;

    printf("Enter an integer: ");
    scanf("%d", n);

    coolfunction(n, &result);

    printf("\n e^%d = %lf \n", n, result);
    return 0;
}

Enable all warnings and read about `scanf`. I'm surprised that it "lets you enter the int". — M Oehm, Jan 03 '18 at 09:38
`result` is of type `double`, but `coolfunction` expects a pointer to `int`. — Patrick Bucher, Jan 03 '18 at 09:43
`scanf("%d", n)` gives undefined behaviour since `n` is not an address of an `int`. Use `scanf("%d", &n)` instead. — Peter, Jan 03 '18 at 09:52
My question is not regarding the reason that '&' had to be used in scanf, so I couldn't have know look for my answer in questions like "Ampersand(&) and scanf in C?" — Emirhan G., Jan 03 '18 at 11:04

Patrick Bucher · Accepted Answer · 2018-01-03T09:57:20.533

1

Here's a version using a double parameter:

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

void coolfunction(int x, double *y)
{
    *y = exp(x);
}

int main()
{
    int n = 0, scanned = 0;
    double result = 0;

    printf("Enter an integer: ");
    scanned = scanf("%d", &n);
    if (scanned < 1) {
        fprintf(stderr, "value entered not a valid integer\n");
        exit(EXIT_FAILURE);
    }
    coolfunction(n, &result);
    printf("\n e^%d = %g \n", n, result);
    return 0;
}

You also missed the & in your scanf call: the function needs to know the address of your variable, not its value.

edited Jan 03 '18 at 09:57

answered Jan 03 '18 at 09:48

Patrick Bucher

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You should check the return value from `scanf` – Ed Heal Jan 03 '18 at 09:52
@EdHeal Good point, did so. – Patrick Bucher Jan 03 '18 at 10:02
Would you also happen to know WHY I can't make the function like `void coolfunction(int x, double & y)` i.e. pass by reference? It works in C++ and it enables one to not deal with dereferencing pointers inside the function. – Emirhan G. Jan 03 '18 at 11:24
@EmirhanG. C doesn't have C++-style references. You either use pointers or or values. – Patrick Bucher Jan 03 '18 at 12:09

Why do I get a segmentation error here in my code?

1 Answers1