# Multiple calculations in 4 processes using fork()

Write a program to create 4 processes: parent process and its child process which perform various tasks :

- Parent process count the frequency of a number
- 1st child sort the array
- 2nd child find total even number(s) in a given array
- 3rd child calculate the sum of even numbers in an array

**Example –**

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Input :2, 4, 6, 7, 9, 0, 1, 5, 8, 3Output :Parent process : the key to be searched is 7 the frequency of 7 is 1 1st child process : the sorted array is 0 1 2 3 4 5 6 7 8 9 2nd child process : Total even no are: 5 3rd child process : the sum is :45

**Explanation –** Here, we had used fork() function to create 4 processes three child and one parent process. So, here we use two fork() function which create 4 process n1=fork() and n2 = fork()

- if n1 and n2 is greater than zero then it is parent process which counts the frequency of a number.
- if n1 is equal to zero and n2 is greater than zero then it is 1st child process which sorts the given array.
- if n1 is greater than zero and n2 is equal to zero than it is 2nd child process which finds the total even numbers in the array.
- if n1 and n2 both equal to zero then it is 3rd child calculates the sum of all elements in an array.

**Code –**

`// C++ code to demonstrate the calculation` `// in parent and its 3 child processes using fork()` `#include <iostream>` `#include <unistd.h>` ` ` `using` `namespace` `std;` ` ` `int` `main()` `{` ` ` ` ` `int` `a[10] = { 2, 4, 6, 7, 9, 0, 1, 5, 8, 3 };` ` ` `int` `n1, n2, i, j, key, c, temp;` ` ` `n1 = fork();` ` ` `n2 = fork();` ` ` ` ` `// if n1 is greater than zero` ` ` `// and n2 is greater than zero` ` ` `// then parent process executes` ` ` `if` `(n1 > 0 && n2 > 0) {` ` ` ` ` `int` `c = 0;` ` ` `cout << ` `"Parent process :"` `<< endl;` ` ` ` ` `// key to be searched is 7` ` ` `key = 7;` ` ` `cout << ` `"the key to be searched is "` `<< key << endl;` ` ` ` ` `for` `(i = 0; i < 10; i++) {` ` ` ` ` `if` `(a[i] == key)` ` ` `// frequency of key` ` ` `c++;` ` ` `}` ` ` ` ` `cout << ` `"the frequency of "` `<< key << ` `" is "` `<< c << endl;` ` ` `}` ` ` ` ` `// else if n1 is zero` ` ` `// and n2 is greater than zero` ` ` `// then 1st child process executes` ` ` `else` `if` `(n1 == 0 && n2 > 0) {` ` ` ` ` `cout << ` `"1st child process :"` `<< endl;` ` ` ` ` `for` `(i = 0; i < 10; i++) {` ` ` ` ` `for` `(j = 0; j < 9; j++) {` ` ` ` ` `if` `(a[j] > a[j + 1]) {` ` ` ` ` `temp = a[j];` ` ` `a[j] = a[j + 1];` ` ` `a[j + 1] = temp;` ` ` `}` ` ` `}` ` ` `}` ` ` ` ` `cout << ` `"the sorted array is"` `<< endl;` ` ` ` ` `for` `(i = 0; i < 10; i++) {` ` ` ` ` `cout << a[i] << ` `" "` `;` ` ` `}` ` ` ` ` `cout << endl;` ` ` `}` ` ` ` ` `// else if n1 is greater than zero` ` ` `// and n2 is zero` ` ` `// then 2nd child process executes` ` ` `else` `if` `(n1 > 0 && n2 == 0) {` ` ` ` ` `int` `f = 0;` ` ` `cout << ` `"2nd child process :"` `<< endl;` ` ` ` ` `for` `(i = 0; i < 10; i++) {` ` ` ` ` `// counting total even numbers` ` ` `if` `(a[i] % 2 == 0) {` ` ` ` ` `f++;` ` ` `}` ` ` `}` ` ` ` ` `cout << ` `" Total even no are: "` `<< f << ` `" "` `;` ` ` `cout << endl;` ` ` `}` ` ` ` ` `// else if n1 is zero` ` ` `// and n2 is zero` ` ` `// then 3rd child process executes` ` ` `else` `if` `(n1 == 0 && n2 == 0) {` ` ` ` ` `cout << ` `"3rd child process :"` `<< endl;` ` ` ` ` `int` `sum = 0;` ` ` `// summing all given keys` ` ` `for` `(i = 0; i < 10; i++) {` ` ` ` ` `sum = sum + a[i];` ` ` `}` ` ` ` ` `cout << ` `"the sum is :"` `<< sum << endl;` ` ` `}` ` ` ` ` `return` `0;` `}` |

**Output –**

Parent process : the key to be searched is 7 the frequency of 7 is 1 1st child process : the sorted array is 0 1 2 3 4 5 6 7 8 9 2nd child process : Total even no are: 5 3rd child process : the sum is :45

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