Can you explain what this programs are doing? [closed] - c++

Question

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
Questions asking for code must demonstrate a minimal understanding of the problem being solved. Include attempted solutions, why they didn't work, and the expected results. See also: Stack Overflow question checklist
Closed 9 years ago.
Improve this question
So I have to do trace tables for this but I don't understand everything from the code such as a==b; c-=--d; b+=a%10
int a=3,b=4, c=5,d=6;
if(a==b)c++;else c--;
while(d>2){
c-=--d; b-=a;
}
int a=3,b=0, c=7,d=5;
if(a=b)d++;else c--;
while(d>2){
c+=a;a+=--d;
}
int a=3,b=11, c=15,d=5;
if(a>b)d--;else c--;
for(;d>3;c/=a){
b=--d;
}
int a=31,b=14, c=95,d=56;
if(a<b)d++;else c--;
while(d>53){
b+=a%10;d--; a/=10;
}

Answer 1

c -= --d;
mean
c = c - (--d);
The same goes for
b += a%10
which mean
b = b + (a%10)
You can do the same with *, / and % operator
--d mean that d is decreased before the instruction get executed, ++d would mean d will be increased before the instruction got executed
if(a==b)c++;else c--;
is the same as the more readable
if (a==b)
{
c = c + 1;
}
else
{
c = c - 1;
}

Answer 2

int a=3,b=4, c=5,d=6;
if(a==b) c++;
else c--;
while(d>2){
c-=--d; b-=a;
}
The == operator means comparasion if a and b are the same. In this case a and b are different, so it goes to the else and decrements the c variable for 1.
The -- after c means that the value is decreased before the instruction gets executed.
So, that means c will become 4.
While d > 2, means it will loop as long as d > 2.
c -= --d; b-=a;
That means:
c = c - --d
b = b - a
So, that means the value of d will decrease by 1 each time the loop is executed and will keep looping until it's >2.
int a=3,b=0, c=7,d=5;
if(a=b)d++;
else c--;
while(d>2){
c+=a;a+=--d;
}
The = operator means to assign a value, so when it executed a=b, it will assign the value of b to a but since it's 0, which means false it will go to else and decrease the value of c by 1.
So c will become 6.
The while loop is similar to the first one.
int a=3,b=11, c=15,d=5;
if(a>b)d--;else c--;
for(;d>3;c/=a){
b=--d;
}
This one is quite simple if-statement. It checks whether a is bigger than b. If so, it executes d--, else c--.
As for the for-loop, it goes until d > 3 and it executes c /= a each time as well.
c /= a also can be written as c = c / a.
int a=31,b=14, c=95,d=56;
if(a<b)d++;else c--;
while(d>53){
b+=a%10;d--; a/=10;
}
The last one if statement is simple as well and similar to the above one.
The while loop will be executed until d > 53.
The command inside b+=a%10;d--; a/=10; can be also written as:
b = b + a % 10
d--
a = a / 10

Answer 3

a==b
This is an important Boolean condition that checks whether a is equal to b and returns true if it is and returns false if it is not. This can be changed (casted) to an int of value 1 or 0.
c-=--d;
I wouldn't prefer writing such code.
However c -= k statement is equivalent to c = c-k
and --d; is same as decrement d by 1.
The code does these two things in one statement. But order is important. Since -- comes before d, first this decrement is evaluated and then the -= operator is considered.
Similarly for +=
I would suggest looking up a good C++ learning resource such as www.cplusplus.com or www.learncpp.com