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Result of sizeof operator
  • Difficulty Level : Hard
  • Last Updated : 31 Jul, 2018
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Predict the output of below program.




#include <stdio.h>
#define TOTAL_ELEMENTS (sizeof(array) / sizeof(array[0]))
int array[] = {1, 2, 3, 4, 5, 6, 7};
  
int main()
{
 int i;
  
 for(i = -1; i <= (TOTAL_ELEMENTS-2); i++)
   printf("%d\n", array[i+1]);
  
 getchar();
 return 0;
}

Output: Nothing is printed as loop condition is not true for the first time itself.

The result of sizeof for an array operand is number of elements in the array multiplied by size of an element in bytes. So value of the expression TOTAL_ELEMENTS in the above program is 7.
The data type of the sizeof result is unsigned int or unsigned long depending upon the compiler implementation. Therefore, in the loop condition i <= (TOTAL_ELEMENTS-2), an int is compared to an unsigned value. int is implicitly converted to unsigned (true for both unsigned int and unsigned long). So -1 ( unsigned equivalent 4294967295 if integers are stored using 32 bit) is compared to TOTAL_ELEMENTS - 2 and the condition is not true for the first time itself.


Please write comments if you find anything incorrect in the above post.

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