user3237895 - 1 year ago 294

C Question

this is PSET 3 from the CS50 course on edX.org.

I have been struggling with this problem set for a very long time; particularly, I cannot get the binarySearch function to work. I keep getting a segmentation fault and I can't figure out how to deal with it. I have spent a lot of time thinking through this and I just don't see it.

Here is my code. Can someone point out conceptually where I am going askew here? Thanks.

`#include <stdio.h>`

#include <cs50.h>

bool binarySearch(int value, int values[], int min, int max)

{

bool answer = false;

if (max < min)

{

answer = false;

}

else if (values[max] == value)

{

answer = true;

}

else if (values[min] == value)

{

answer = true;

}

else

{

int midPoint = (max + min) / 2;

if (values[midPoint] == value)

{

answer = true;

}

else if (values[midPoint] > value)

{

answer = binarySearch(value, values, min, midPoint);

}

else

{

answer = binarySearch(value, values, midPoint, max);

}

}

return answer;

}

int main (int argc, char *argv[])

{

int value = 34;

int values[] = {11,22,33,44,55,66,77,88,99,1010};

int max = sizeof(values) / sizeof(int);

if (binarySearch(value, values, 0, max - 1))

{

printf("Found needle!\n");

}

else

{

printf("Did not find needle\n");

}

}

I keep getting a segmentation fault when the value I am searching for is not in the array.

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Answer Source

I think you should change you code to:

```
else
{
int midPoint = (max + min) / 2;
if (values[midPoint] == value)
{
answer = true;
}
else if (values[midPoint] > value)
{
answer = binarySearch(value, values, min, midPoint-1); // not midPoint
}
else
{
answer = binarySearch(value, values, midPoint+1, max); //not midPoint
}
}
```

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