Can you explain the output of below C++ program ?

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Why is the output of the above program is 

  • 5 : 1 : 20
  • 1 : 1 : 50
  • 5 : 2 : 50
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CppFreak (anonymous) 0 Comments

Let’s try to dissect this C++ program step by step

TEACHER T(5), M

 

The above initializes a teacher object T with values Tid = 5, TeachCode = 0 and TeacherCount = 0

 

 

This will initialize M with values Tid = 1 (default value assigned in the constructor) TeachCode = 0 and TeacherCount = 0 —————————- (A)

 

When we call the function T.subject() which basically has the below code

 

void Subject(int S = 20) {
    TeachCode++;
    TeacherCount += S;
}

 

The function increments TeachCode by 1 to give it’s value TeachCode = 1 and TeacherCount+= S will give it’s value TeacherCount = 20 as it’s initial value is 0.

Hence the first call prints 5 : 1 : 20 ———————————– (1)

 

calling M.subject(50) will change the values of TeachCode and TeacherCount which is dependent on the value of S which is initialized with a value of 50 via the function argument. Now since Tid in this case is already 1 from equation (A) above, it prints the output 1 : 1 : 50  ———————————– (2)

 

 

 

First invocation of T.subject() already changed the values of Tid, TeachCode and TeacherCount as 5, 1 and 20 respectively.

Calling subject() again via T.subject(30) will again update the values as 

Tid = 5 (which isn’t modified in the subject function).

Since TeachCode was 1 initially, TeachCode++ will change it’s value to 2

Also TeacherCount was = 20 due to the first invocation of T.subject();

hence calling T.subject(30) this time will add 30 to it’s initial value giving it’s new value of 20+30 = 50

 

Hence the final call to subject will print 5 : 2 : 50 ———————————– (3)

 

 

Hope this clearly explains the behavior

 

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