I need help with tracing.

I need help with tracing two programs:

#include <iostream>
using namespace std;
int func(int p, int q);
int main()
{
     int a = 1, b = 6, c = 4;

     c = func(a,b);
     cout << "in main: " << a << " "
          << b << " " << c << endl;
     c = func(2,a+b) + 100;
     cout << "in main again: " << c << endl;
     cout << "over";
     return 0;
}

int func(int p, int q)
{
     int r, s;

     r = p + q;
     if (r == 7)
          s = r + 3;
     else
          s = r - 5;
     cout << "in the func: " << p << " " << q
          << " " << r << " " << s << endl;
     return r + s;
}

My output is
in the func: 1 6 7 10
in main: 1 6 17
in function 2 7 9 4
in main again: 113
over

I have the correct output but I don't understand how does it go from 1 6 7 10 to 1 6 17 then to 2 7 9 4.

#include <iostream>
using namespace std;
int main()
{
     int p = 10, r = 6, s = 2;

     for (p = 1; p < 4; p++) {
          cout << "type in a number";
          if (p < 3)
              cin >> r;
          else
              cin >> s;  
          cout << "in: " << p << " "
               << r << " " << s << endl;
     }
     cout << "out";
     return 0;
}

For this program, I am suppose to enter 10, 20, 30.

My output is:
1 10 2
2 20 2
3 20 30

How did it go from 2 20 2 to 3 20 30 when the formula in the program doesn't even have calculations.

pogrady (677)

loop iteration one:

p = 1
r = 10
s = 2

loop iteration 2
p =2
r = 20
s = 2

loop iteration 3
p = 3
r = 20
s = 30

whats wrong?

Last edited on

bainofmyexistance (21)

I am using codeblocks

Edit: I don't understand how does R become 20 and S becomes 30.

Last edited on

monad (49)

Hopefully this will help with the second one:

Line Notes                 Values
-----------------------------------------
  5: initialization      | p=10 r=6  s=2

  7: p is set to 1       | p=1  r=6  s=2
  7: p < 4 is true       | ""
  9: p < 3 is true       | ""
 10: user sets r to 10   | p=1  r=10 s=2
 13: output 1, 10 and 2  | ""

  7: p is incremented    | p=2  r=10 s=2
  7: p < 4 is true       | ""
  9: p < 3 is true       | ""
 10: user sets r to 20   | p=2  r=20 s=2
 13: output 2, 20 and 2  | ""

  7: p is incremented    | p=3  r=20 s=2
  7: p < 4 is true       | ""
  9: p < 3 is false      | ""
 12: user sets s to 30   | p=3  r=20 s=30
 13: output 3, 20 and 30 | ""

  7: p is incremented    | p=4  r=20 s=2
  7: p < 4 is false      | ""
 16: output "out"        | ""

The first looks more complicated, but I may take a look at it later.

Edit: Fixed an incorrect line number.

Last edited on

bainofmyexistance (21)

Thanks so much! I eventually figured out how the first one works.

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I need help with tracing.