Exercise 5.2 Summing 100 data values

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Exercise 5-2. Define an array, data, with 100 elements of type double. Write a loop that
will store the following sequence of values in corresponding elements of the array:

1/(2*3*4) 1/(4*5*6) 1/(6*7*8) ... up to 1/(200*201*202)

Write another loop that will calculate the following:

data[0] - data[1] + data[2] - data[3] + ... -data[99]

Multiply the result of this by 4.0, add 3.0, and output the final result. Do you recognize the
value you get?

 1 //Exercise 5.2 Summing 100 data values 2 #include <stdio.h> 3  4 int main(void) 5 { 6   double data[100];                    // Stores data values 7   double sum = 0.0;                    // Stores sum of terms 8   double sign = 1.0;                   // Sign - flips between +1.0 and -1.0 9   size_t i = 0;10 11   int j = 0;12   for( i = 0 ; i < sizeof(data)/sizeof(double) ; ++i)//神馬意思？13   {14     j = 2*(i + 1);15     data[i] = 1.0/(j * (j + 1) * (j + 2));16     sum += sign*data[i];17     sign = -sign;18  }19 20    // Output the result21   printf("The result is %.4lf\n", 4.0*sum + 3.0);22   printf("The result is an approximation of pi, isn‘t that interesting?\n");23     return 0;24     }

 

Exercise 5.2 Summing 100 data values