Comp Sci Difference between some if statements C++

[asz304]

Say for example

 int a = 0; 
if ( a ){
...
}


int a = 0;
if ( a < 0 ){
...
}

What's different with the first if statement? or do they have the same meaning?

Thanks

EDIT: What is the use of two-dimensional arrays? I see it mostly in file input output stream stuff.

And how do I change the brightness of a picture using c++ using this formula:

R2 = G2 = B2 = (R1 + G1 + B1)/3

Do I need to use pass by reference?

 

[NobodySpecial]

In this case nothing, the loop doesn't execute for a=0

The first one will execute for any value of 'a' other than 0, the second will execute for any negative 'a'

 

[Mark44]

Say for example

 int a = 0; 
if ( a ){
...
}


int a = 0;
if ( a < 0 ){
...
}

What's different with the first if statement? or do they have the same meaning?

Thanks

EDIT: What is the use of two-dimensional arrays? I see it mostly in file input output stream stuff.

Two-dimension arrays are useful if you have information that's in tables. One application of arrays like this is in graphics. Years ago you could write programs that would store strings of bytes to a particular location in memory that would change what was on the computer screen. Different modes (such as text vs. high resolution graphics) used memory at different locations and different amounts of memory. The screen is two-dimensional, with each row of letters or pixels corresponding to a row in a two-D array. A program could initialize an array and write it to memory and the screen would change.

And how do I change the brightness of a picture using c++ using this formula:

R2 = G2 = B2 = (R1 + G1 + B1)/3

Do I need to use pass by reference?

You need to use some graphics library that has functions that change what is displayed on the screen, change the brightness, and so on. I would have to know more about what is available in the graphics package to be able to answer your question.

 

[Lednakashim]

Say for example

EDIT: What is the use of two-dimensional arrays? I see it mostly in file input output stream stuff.

And how do I change the brightness of a picture using c++ using this formula:

R2 = G2 = B2 = (R1 + G1 + B1)/3

Do I need to use pass by reference?[/QUOTE]

1. 2D arrays are a representation of a discrete surface: most commonly a grid. The game board of battleship comes to mind as does [PLAIN]"[URL[/PLAIN]  Game of Life[/URL], and off-course an pixel map.

2. Thats a strange formula, its probably wrong. The higher the number for each color the closer it is to white. SO, 255-255-255 is white and 000-000-000 is black. Its possible to make things whiter/lighter(?) by addition of positive increments. 

3. I don't know do you? Probably or else the changes won't carry over in the function output.