keeps saying Segmentation fault - c

Question

This code keeps saying segmentation fault.
for(i=0; i<(numTopps-1); i++)
{
if(kcalTopp[i]<kcalTopp[i+1])
{
temp=*kcalTopp[i];
*kcalTopp[i]=*kcalTopp[i+1];
*kcalTopp[i+1]=temp;
}
}
I think above part is a problem.
but I can't figure what is the problem
#include <stdio.h>
#include <stdlib.h>
void sort(int *kcalTopp[], int numTopps);
int main(void)
{
int numTopps, doughPrice, eachToppPrice, kcalDough, i, j, totalKcal, highest, kcalperDol;
scanf("%d %d %d %d", &numTopps, &doughPrice, &eachToppPrice, &kcalDough);
int *kcalTopp;
kcalTopp=(int*)malloc(sizeof(int)*numTopps);
for(i=0; i<numTopps; i++)
{
scanf("%d", &kcalTopp[i]);
}
totalKcal=kcalDough;
highest=totalKcal/doughPrice;
sort(&kcalTopp, numTopps);
for(i=0; i<numTopps; i++)
{
for(j=0; j<=i; j++)
{
totalKcal=totalKcal+kcalTopp[j];
kcalperDol=totalKcal/(doughPrice+i*eachToppPrice);
if(kcalperDol>highest)
{
highest=kcalperDol;
}
}
}
printf("%d", highest);
return 0;
}
void sort(int *kcalTopp[], int numTopps)
{
int temp, i;
for(i=0; i<(numTopps-1); i++)
{
if(kcalTopp[i]<kcalTopp[i+1])
{
temp=*kcalTopp[i];
*kcalTopp[i]=*kcalTopp[i+1];
*kcalTopp[i+1]=temp;
}
}
}

Answer 1

Indeed, your problem is the sort function you described, as you suspected. Are you aware what *kcalTopp[i]=*kcalTopp[i+1]; does exactly? You get as parameter an int *array[] which is equivalent to int **array (you can see it as an array of arrays of ints). So when you tell C to access array[i] you will access the i-th array. This is a pointer, and in fact *kcalTopp[i] will be the first element from the i-th array. What you are doing here is swapping first elements from the arrays, but in practice you have a single array of ints (or more technically, an array of length 1 of arrays). The simplest fix is to write:
temp=(*kcalTopp)[i];
(*kcalTopp)[i]=(*kcalTopp)[i+1];
(*kcalTopp)[i+1]=temp;
just to change the precedence of the operators. Now, what we achieved is: we take the first array from the array list (it's the only one we have, isn't it?) with (*kcalTopp); this is an int *, not int ** anymore. Now you can safely access the i-th element from it.
Without parentheses, you would first access the i-th array, because in *kcalTopp[i], the [i] part will execute before the * part.
Anyway, to simplify things, you are not required to take as parameter an int *kcalTopp[], you can simply take int kcalTop[] or int *kcalTopp and not use * anymore:
temp = kcalTopp[i];
kcalTopp[i] = kcalTopp[i+1];
kcalTopp[i+1] = temp;

Answer 2

The original code in your post is using an extra (unnecessary) layer of indirection for kcalTopp, resulting in attempts to manipulate an array of addresses (pointers) as opposed to manipulating int values pointed to in memory. This in turn is likely to be the reason you are seeing segmentation faults, which occur when attempting to access memory that you do not own. For some input values, and depending on what day you run your program, it may run, and it may crash.
(This is sometimes referred to as undefined behavior, and is the reason that the problem will not always manifest itself, making you think your program is flawless, when it is not.)
The following contains edits to your original code for the purpose of illustrating some of the suggestions in comments. (not to fix every logic error.) The edits do include treating kcalTopp as a pointer to int memory as opposed to an array of int *. See in-line comments for clarifications:
//void sort(int *kcalTopp[], int numTopps);//*kcalTopp[] is an array of pointers
void sort(int *kcalTopp, int numTopps);//*kcalTopp is a pointer to 'int' memory
int main(int argc, char *argv[])
{
int numTopps, doughPrice, eachToppPrice, kcalDough, i, j, totalKcal, highest, kcalperDol;
//scanf("%d %d %d %d", &numTopps, &doughPrice, &eachToppPrice, &kcalDough);
if(argv != 5) //simple reading in of command line args
{
printf("4 input values required. Exiting");
return 0;
}
//note, each of these calls includes simple for test for success before going on
numTopps = strtol(argv[1], (char **) NULL, 10);
if(errno == ERANGE) {printf("argv[1] Bad input, exiting"); return 0;}
doughPrice = strtol(argv[2], (char **) NULL, 10);
if(errno == ERANGE) {printf("argv[2] Bad input, exiting"); return 0;}
eachToppPrice = strtol(argv[3], (char **) NULL, 10);
if(errno == ERANGE) {printf("argv[3] Bad input, exiting"); return 0;}
kcalDough = strtol(argv[4], (char **) NULL, 10);
if(errno == ERANGE) {printf("argv[4] Bad input, exiting"); return 0;}
int *kcalTopp;
//This statement (without cast) is sufficient to create memory for kcalTopp
kcalTopp = malloc(sizeof(int)*numTopps);
if(!kcalTopp)//should always test before using memory
{
printf("memory allocation failed, exiting");
return 0;
}
for(i=0; i<numTopps; i++)
{
scanf("%d", &kcalTopp[i]);
}
totalKcal=kcalDough;
highest=totalKcal/doughPrice;
//sort(&kcalTopp, numTopps);
// ^ not needed
sort(kcalTopp, numTopps);
for(i=0; i<numTopps; i++)
{
for(j=0; j<=i; j++)
{
totalKcal=totalKcal+kcalTopp[j];
kcalperDol=totalKcal/(doughPrice+i*eachToppPrice);
if(kcalperDol>highest)
{
highest=kcalperDol;
}
}
}
printf("%d", highest);
return 0;
}
void sort(int *kcalTopp, int numTopps)//note removal of []
{
int temp, i;
for(i=0; i<(numTopps-1); i++)
{
if(kcalTopp[i]<kcalTopp[i+1])
{
temp=kcalTopp[i];//note removal of '*' from all kcalTopp
kcalTopp[i]=kcalTopp[i+1];
kcalTopp[i+1]=temp;
}
}
}