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//I suggest using strlen (of #include<string.h>)
//if you want only the size of the occupied index
int prices[5] = { 1, 2, 3, 4, 5 };
int size = strlen((char*)prices); // convert it to string
printf("%d", size+1); // Just add 1 that's it
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int prices[5] = { 1, 2, 3, 4, 5 };
int size = sizeof prices / sizeof prices[0];
printf("%u", size); /* 5 */