Error in array allocation in C

Question

i've try to compile this simple program, it will alloc a dyamic array and return it with a multiple of 5 in every location. but it doesn't work, it report me an error in the pointer.

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

int main(int argc, char const *argv[]) {
    int n;
    int i;
    int* ptra;
    scanf("%d", &n);
    ptra = malloc(n*(sizeof(int)));

    for(i=0; i<=n; i++){
        ptra[i] = (5*(i+1));
        printf("%d\n", ptra[i]);
    }
    return 0;
}

An array of n integers contains elements in the range from 0 to n - 1. Now take a look at your loop again, and think about that loop condition. — Some programmer dude
– Some programmer dude, Commented Nov 30, 2016 at 10:35
Please elaborate on "doesn't work". If it doesn't build then please include the build errors. If it crashes then use a debugger to locate where in your code it happens. If you get unexpected output then include the input and the expected and actual output. — Some programmer dude
– Some programmer dude, Commented Nov 30, 2016 at 10:43
In that case I think you should delete the question, as it's not really useful in its current form. — Some programmer dude
– Some programmer dude, Commented Nov 30, 2016 at 10:50

Jonathan Leffler · Accepted Answer · 2017-09-14 03:32:11Z

3

Index range for ptra must be from 0 to n-1 (both inclusive). But here:

for(i=0;i<=n;i++){

you are going out of bounds, which is undefined behaviour. Change it to:

for(i = 0; i < n; i++) {

Note: Always check the return of all the standard functions for failures (scanf() and malloc() in your code).

edited Sep 14, 2017 at 3:32

Jonathan Leffler

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answered Nov 30, 2016 at 10:36

P.P

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3 Comments

P.P Over a year ago

Did you add the error checking I suggested? Please describe what "doesn't work". It works as expected.

fenigo69 Over a year ago

the compiler compile the program, but when i'm going to run it,report me "the program It is not recognized as executive program or a batch file"

P.P Over a year ago

That appears to a problem with your environment. Check your PATH is correct. See this and related posts linked in that page.

ΦXocę 웃 Пepeúpa ツ · Accepted Answer · 2016-11-30 10:43:55Z

0

Your for loop is going one step beyond the limit: must go as long as i<n and not i<=n

try doing:

for(i=0; i<n; i++){

edited Nov 30, 2016 at 10:43

answered Nov 30, 2016 at 10:38

ΦXocę 웃 Пepeúpa ツ

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1 Comment

fenigo69 Over a year ago

it report me "the program It is not recognized as executive program or a batch file"

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