Segmentation fault: 11 on c program

Question

In my code:

int nAlunos, nNotas;

/*size input*/

scanf("%d", &nAlunos);

scanf("%d", &nNotas);

/*arrays*/

int ordenador [nAlunos];
char listaNomes [nAlunos][16];
float listaNotas [nAlunos][nNotas+1];

/*non-arrays*/

int i, k;

/*input*/

for(i = 0; i < nAlunos; i++){
    scanf("%s", listaNomes[i]);
    for(k = 1; k <= nNotas; k++){
        scanf("%f", &listaNotas[i][k]);
    }
}


/*sum of grades / number os grades for each person*/

for(i = 0; i < nAlunos; i++){
    listaNotas[i][0] = 0;

    for(k = 1; k <= nNotas; k++)
        listaNotas[i][0] += listaNotas[i][k];

    listaNotas[i][0] /= nNotas;
}


/*process order on vector*/

for(i = 0; i < nAlunos; i++){
    menor = 1111;

    for(k = i; k < nAlunos; k++)
        if (listaNotas[k][0] < menor)
            menor = listaNotas[k][0];

    for(k = i; listaNotas[k][0] != menor; k++){}

    ordenador[k] = i;
    ordenador[i] = k;
}
for(i = 0; i < nAlunos; i++)
    printf("%d", ordenador[i]);

}

I am trying to fill a table of data from the user, I may not use pointers for this class.

it needs to receive data as presented:

String1
float1 float2...
String2
.
.
.

When running it, it works well until I finish with the last input. After that it just breaks the execution and returns me segmentation fault: 11

I tried to find where could it be accessing improper memory, but it just doesn't make sense to me because I cannot find it.

Answer 1

Here's a simple adaptation of your code, with error checking on the scanf() calls:

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

static void err_exit(const char *msg);

int main(void)
{
    int nAlunos, nNotas;

    if (scanf("%d", &nAlunos) != 1 || scanf("%d", &nNotas) != 1)
        err_exit("failed to read dimensions");

    char listaNomes[nAlunos][16];
    float listaNotas[nAlunos][nNotas+1];
    int i, k;

    for (i = 0; i < nAlunos; i++)
    {
        if (scanf("%s", listaNomes[i]) != 1)
            err_exit("failed to read name");

        for (k = 1; k <= nNotas; k++)
        {
            if (scanf("%f", &listaNotas[i][k]) != 1)
                err_exit("failed to read grade");
        }
    }

    for (i = 0; i < nAlunos; i++)
    {
        printf("%s:", listaNomes[i]);
        for (k = 1; k <= nNotas; k++)
            printf(" %f", listaNotas[i][k]);
        putchar('\n');
    }
    return 0;
}

static void err_exit(const char *msg)
{
    fprintf(stderr, "%s\n", msg);
    exit(1);
}

Given the input file:

3
4
name-the-first
12 13 14 15
name-the-second
21 22 23 24
name-the-third
31 310 3109 31098

The output from the program is:

name-the-first: 12.000000 13.000000 14.000000 15.000000
name-the-second: 21.000000 22.000000 23.000000 24.000000
name-the-third: 31.000000 310.000000 3109.000000 31098.000000

This is what should be expected.

The only oddity in the code is the use of for (k = 1; k <= nNotas; k++) because it leaves listaNotas[i][0] uninitialized and unused. You did, however, allocate enough space so that isn't a cause of trouble.

Summary

The problem is not self-evidently in the code you showed. Please show the actual code that crashes!

Answer 2

for(k = i; listaNotas[k][0] != menor; k++){}

The above statement is causing the out of bound access of the array! Hence the segmentation fault . Handle it according to your functionality.

The condition listaNotas[k][0] != menor is fatal.