c언어 초보 질문합니다!

아래 코드에서 pop이 l-value여야한다는데 이것이 무엇인지 잘 모르곘습니다.

#define _CRT_SECURE_NO_WARNINGS
#include
#include
#include

typedef struct _popularity_t {
int rank;
int cnt;
char name[32];
} popularity_t;

int main(void) {
FILE* fp;
char* fname = "popular_names.txt";
popularity_t pop[20];
int i = 0;
int op; int search_rank; char search_name[32];
int N;
void* memset(void* pop, int N, size_t count);
printf("Input N");
scanf("%d", &N);

pop = (popularity_t *)malloc(sizeof(popularity_t));

fp = fopen(fname, "r");
if (fp == NULL) {
printf("Error in %s\n", fname);
return -1;
}
while (i < N && (fscanf(fp, "%d %s %d", &pop[i].rank, pop[i].name, &pop[i].cnt)) != EOF)
i++;

if (i < N) {
N = i;
pop = (popularity_t*)realloc(pop, sizeof(popularity_t) * N);
}

fclose(fp);

printf("Searching(1:rank, 2:name): ");
scanf("%d", &op);
switch (op) {
case 1:
printf("Input rank: "); scanf("%d", &search_rank);
for (i = 0; i < 20; i++){
if (search_rank == pop[i].rank) {
printf("%d %s %d \n", pop[i].rank, pop[i].name, pop[i].cnt);
}
}
break;
case 2:
printf("Input name: ");
scanf("%s", search_name);
for (i = 0; i < N; i++) {
if (strcmp(search_name, pop[i].name) == 0) {
printf("%d %s %d \n", pop[i].rank, pop[i].name, pop[i].cnt);
}
}
break;
}

free(pop);

return 0;
}