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C linear search error
#include <stdio.h>
#include <string.h>
#define PF printf
int main() {
    int intcmp(void *ip1, void * ip2);
    void * lsearch(void *key, void *base, int n, int elemSize,
                   int(* cmpfun)(void *, void *));
    int arr[] = {4, 6, 2, 3, 11, 22, 15};
    int n = sizeof(arr) / sizeof(int);
    int key = 11;
    int *found = lsearch(&key, &arr, n, sizeof(int), intcmp);
    PF("found=%p", found);
    return 1;
}
int intcmp(void *ip1, void * ip2) {
    int *p1 = ip1;
    int *p2 = ip2;
    return *p1 - *p2 == 0;
}
void * lsearch(void *key, void *base, int n, int elemSize,
               int(* cmpfun)(void *, void *)) {
    int i;
    for(i = 0; i < n; i ++) {
        void *elemArr = (char *)base + i * elemSize;
        if(cmpfun(key, elemArr) == 0)
            return elemArr;
    }

    return NULL;
}

if(cmpfun(key, elemArr) == 0)
        return elemArr;

return *p1 - *p2 == 0;

#include <stdio.h>
#include <string.h>

// This is bad practice. It makes your code less readable.
// I won't use it below.
#define PF printf

// Declare this first so a prototype is not needed.
// You violated a C pattern by using `cmp` in the name.
// Comparison functions in C return <0, 0, >0, not a binary value.
// To wit, later you used the comparison correctly.  I've fixed the
// inconsistency.
int intcmp(void *vp1, void *vp2)
{   // Most C styles have the brace on its own line, unlike Java. Roll with it.
    int *p1 = vp1, *p2 = vp2;
    return *p1 - *p2;
}

// Search n elements of size elemSize in the array at
// base in sequence using cmpfun on key,
// to test for equality (cmpfun == 0).  Return a pointer
// to the found element or NULL if none.
void *lsearch(void *key, void *base, int n,
              int elemSize, int(* cmpfun)(void *, void *))
{
    int i;

    for (i = 0; i < n; i++) {
        void *elemArr = (char*)base + i * elemSize;
        if (cmpfun(key, elemArr) == 0)
            return elemArr;
    }
    return NULL;
}

int main()
{
    int arr[] = {4, 6, 2, 3, 11, 22, 15};
    int n = sizeof(arr) / sizeof(int);
    int key = 11;
    int *found = lsearch(&key, &arr, n, sizeof(int), intcmp);
    printf("found=%p (%d)", found, *(int*)found);
    return 0; // By convention zero corresponds to no error.
}