“Error Segmentation fault (core dumped)” while working with Arrays in C

Question

I have this code and it works perfectly fine except when my input is the number "2" .

I don't know why, the code seems ok... Is there something wrong?

void initValue(int *a, int dim, int value, int i);
int findValue(int *a, int dim, int value, int i);

main(){
    int i, value, dim = 5;
    int a[dim];

    initValue(a, dim, value, i);

    printf("\nYour values are: ");
    for(i = 0; i < dim; i++) printf("%d ", a[i]);
    printf("\n\n");
}

void initValue(int *a, int dim, int value, int i){
    printf("Insert your values:\n");

    for(i = 0; i < dim; i++){
        scanf("%d", &value);
        if(findValue(a, dim, value, i) == 1){
            printf("This value already exist, please insert a new one.\n");
            i--;
        }
        else a[i] = value;
    }
}

int findValue(int *a, int dim, int value, int i){
    int j, result = 0;
    for(j = 0; j < i || a[j] != value; j++) if(a[j] == value) result = 1;

    return result;
}

Answer 1

1. You have to check that scanf() did succeed, something like

    if (scanf("%d", &value) != 1) maybeRemoveAllWhitespacesAndScanfAgain_MaybeReturnWithAnError(); 

2. You decrement i and never check if i < 0

    for(i = 0; (i < dim) && (i >= 0) ; i++){ 

3. initValue() could be defined as

    void initValue(int *a, int dim) { int value; int i; . . . } 

there is no point in passing the variables from main() .

One more thing, if you initialize value before scanf() you can prevent trying to access it while uninitialized.

Answer 2

The error in your code is a logic error in this line:

for(j = 0; j < i || a[j] != value; j++) if(a[j] == value) result = 1;

Say you have dim=5 and i=2 and value=10 , which is not there is a . The loop will not stop at j=2 because a[j] != value is true. After that you are entering undefined behavior territory.

That line needs to be changed to:

for(j = 0; j < i ; j++) if(a[j] == value) return 1;

The function can now be simplified to:

int findValue(int *a, int dim, int value, int i){
   int j = 0;
   for(j = 0; j < i ; j++)
   {
      if(a[j] == value)
      {
         result = 1;
      }
   }
   return 0;
}