// Program 2 : Read(Input) values and Calculate Average

// sentinel value is -1

#include <stdio.h>

// function main begins program execution

int main ( void ) {

// define variables

int i; // input count

int value;

int sum;

float average; // average is floating-point number

// initialize

i = 0 ;

sum = 0 ;

// program introduction

printf("*******************************************************************************\n");

printf("Program Introduction\n");

printf("*******************************************************************************\n");

printf("This program calculate integers average.\n");

printf("Do not enter zero or negative value. (Use only positive integer.)\n");

printf("If you enter value for -1, the input phase is end\n");

printf("and result(average) will be come out.\n");

printf("*******************************************************************************\n\n");

// first read value

printf("Input Value : ");

scanf("%d", &value);

// sentinel value is -1 >>> if value is -1, end input 

// error case 1 >>> if value is -1 and i is 0, print error message 1

// error case 2 >>> if value is not legitimate (zero or negative except -1), print error message 2

while ( value >= 0 ) {

sum += value ; // add value to sum

++i ; // increment count

// next read value

printf("Input Value : ");

scanf("%d", &value);

} // end while

/********************************* termination conduct *********************************/

/***** error case 1 *****/

if ( ( value == -1 ) && ( i == 0 ) ) { 

printf("\n[ERROR 1] You didn't input value\n"); // print error message 1

} // end if

/***** error case 2 *****/

else if ( value != -1 ) { 

printf("\n[ERROR 2] Input Error - Don't input negative or zero\n"); // print error message 2

} // end else if

/***** no error *****/

else { 

// calculate average

average = (float)sum / i ;

// print result(average) - precision is .2

printf("\nAverage is %.2f\n\n", average);

} // end else

return 0; // terminate program successfully

}