Code Complexity 101

Code Complexity 101

Arun Saha, Ph.D.

arunksaha AT gmail DOT com

(A pragmatic programmer and a software craftsman)

https://www.linkedin.com/in/arunksaha

Complexity Kills

What

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Sphaghetti Junction

(Bitter) Fact of life: Code complexity keeps increasing

What

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(Bitter) Fact of life: Code complexity keeps increasing

What

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How to measure code complexity

objectively?

Simple Objective Metric: Cyclomatic Complexity

What

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Developed by Thomas J. McCabe Sr. in 1976 Also known as McCabe Complexity

Definition and Theory: http://en.wikipedia.org/wiki/Cyclomatic_complexity

Informally,

Complexity of a function: # of independent control paths

The minimum is 1, when there is exactly one path.

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What

Informally,

Complexity of a module:

sum of complexities of its functions

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What

Complexity of a function: # of independent control paths

How

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Approximately,

Sum of occurrence of the conditionals that influence the control flow.

For example, in C and C++, each of the following keywords increase the complexity by 1

return, if, for, while, &&, ||, ?:, case,

goto, break, continue

FYI

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however, Calling function does not increase complexity of either

the caller or the callee

FYI

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however, Calling function does not increase complexity of either

the caller or the callee

Example 1

// Two functions of complexity 1

int c1_direct( int x ) {

return x + 1;

}

int c1_redirect( int x ) {

int const result = add( x, 1 );

return result;

}

E.g.

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Example 2

// complexity: 2

// 1 for “return”, 1 for “?:”

int c2_min( int x, int y ) {

return y < x ? y : x;

}

E.g.

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Example 3

// complexity: 3

// 1 for “if”, 1 for each “return”

int c3_min( int x, int y ) {

if( y < x ) {

return y;

}

else {

return x;

}

}

E.g.

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Example 4

// complexity: 3

// 1 for “return”, 1 for “&&”, 1 for “?:”

int c4_bothtrue( int x, int y ) {

return (x && y) ? 1 : 0;

}

E.g.

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Same function can be (correctly) written with different complexities.

FYI

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Example 5.1

Problem BothNonZero: Given two int’s, return

non-zero if both are non-zero, zero otherwise.

// BothNonZero: Approach 1, Complexity: 4

int bothNonZero_1( int x, int y ) {

if( x ) {

if( y ) {

return 1;

}

}

return 0;

}

E.g.

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Example 5.2

// BothNonZero: Approach 2, Complexity: 4

int bothNonZero_2( int x, int y ) {

if( x && y ) {

return 1;

}

return 0;

}

E.g.

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Example 5.3

// BothNonZero: Approach 3, Complexity: 2

int bothNonZero_3( int x, int y ) {

return x && y;

}

E.g.

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FYI

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A common application is to compare the measured complexity against a set of threshold values. One such

threshold set is as follows

Cyclomatic Complexity Risk Evaluation

1 – 10 A simple program, without much risk

11 – 20 More complex, moderate risk

21 – 50 Complex, high risk program

51 + Unstable program (very high risk)

Source: http://www.sei.cmu.edu/reports/97hb001.pdf p. 145

Fine, but how complex is really complex?

FYI

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I use CCCC http://sourceforge.net/projects/cccc/files/cccc/3.1.4/

with my simple wrapper mccabe.sh

(available at) https://github.com/arunksaha/complexity (contains the function examples used here)

Great, how can I get started today?

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