Sides of a Triangle (or Right Triangle) - c

Question

float a, b, c;
printf( "Enter three nonzero values:\n" );
scanf( "%f%f%f", &a, &b, &c );
When I input a = 2, b = 2, and c = 4, why does...
if( a < ( b + c ))
{
if( b < ( a + c ))
{
if( c < ( a + b ))
{
printf( "This is a triangle." );
}
else
{
printf( "This is not a triangle." );
}
}
}
return 0;
}
...print "This is not a triangle" but...
if( a < ( b + c ))
{
if( b < ( a + c ))
{
if( c < ( a + b ))
{
printf( "This is a triangle." );
}
}
}
else
{
printf( "This is not a triangle." );
}
...does not? A solution I am looking at uses the latter code. However, the line where "This is not a triangle" should be is just blank in my command propt when I run the program.
I am using notepad++ with Developer Command Prompt for VS 2019.
vvvvvvv SOLVED vvvvvvvv
This is how I solved the exercise if anyone at the same learning stage as me is interested. I am using a book to learn c programming and I've only read three chapters. Therefore, I wanted to use only what I have learned from the first three chapters.
float a, b, c, temp, no = 0, count = 1;
printf( "Enter three nonzero values:\n" );
scanf( "%f%f%f", &a, &b, &c );
while ( count < 3 ) {
if(a + b > c){
/* Switch place of a and b */
temp = a;
a = b;
b = temp;
/* Switch place of b and c */
temp = c;
c = b;
b = temp;
count++;
}
else {
no++;
/* Switch place of a and b */
temp = a;
a = b;
b = temp;
/* Switch place of b and c */
temp = c;
c = b;
b = temp;
count++;
}
}
if ( no > 0 ) {
printf ( "This is not a valid triangle." );
}
else {
printf ( "This is a valid triangle." );
}
return 0;
This solution uses a while loop to determine if the sides of a triangle can be a valid triangle. I use variable temp to switch places of the sides and then add one to variable no if one of the combinations is not a valid triangle.
I also want to add that the solution for this exercise on chegg.com is false. It confused me a lot.
vvvvvvvv ANOTHER SOLUTION vvvvvvv
The next exercise in my book was to calculate if three values could be the sides of a right triangle. When I solved this I realized that the same code could be used for a regular triangle, too.
float a, b, largest, temp;
printf( "Enter three nonzero values:\n" );
scanf( "%f%f%f", &largest, &a , &b );
if ( a > largest ) {
temp = largest;
largest = a;
a = temp;
}
if ( b > largest ) {
temp = largest;
largest = b;
b = temp;
}
/* a + b > largest if it's a regular triangle */
if ( a * a + b * b == largest * largest ) {
printf( "This is a valid right triangle" );
}
else {
printf( "This is not a valid right triangle" );
}
return 0;
So instead of looping, just compare the variables a and b with largest to find out which variable is largest. And then use the pythagorean theorem to find out if the sides can represent a right triangle, or the a + b > c if the it is a regular triangle.
I prefer this way rather than using unnecessary looping.

Answer 1

Because this is false: if( c < ( a + b )) since 4 < (2 + 2) is false. Therefore the else branch will executes. In your second variant it will only print "This is not a triangle." when the first if is false otherwise not. Try this
if ( (a < ( b + c )) && (b < ( a + c )) && (c < ( a + b )) )
printf( "This is a triangle.");
else
printf( "This is not a triangle.");
Note: This would also print "This is not a triangle." since by your logic with those values it is not a triangle anyway.

Answer 2

You are missing a bracket
if( c < ( a + b ))
{
printf( "This is a triangle." );
}else {
printf( "This is not a triangle." );
}
If wasn't closed before else

Answer 3

Notice the curly brackets and indentation.
In the 1st example:
if(...)
if(...)
if( c < ( a + b ))
{
printf( "This is a triangle." );
}
else
{
printf( "This is not a triangle." );
}
In order to get to the third if statement, the previous two ifs (the first AND the second if) have to be true. Our third if statement has an else branch, which will execute if the third condition is false.
In the 2nd example:
if( a < ( b + c ))
{
// some more code
}
else
{
printf( "This is not a triangle." );
}
else branch will execute only if the first condition is false. If the first condition is true, this else will never be executed.
That being said, the first example translates to:
If a is less than b+c AND b is less than a+c AND c is less than a+b
Then this is a triangle
Else this is not a triangle
The second example translates to:
If a is less than b+c
Then check other conditions
Else this is not a triangle
As a side note, be careful when comparing float numbers