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EMT 101 – Engineering Programming

Week 2. EMT 101 – Engineering Programming. Dr. Farzad Ismail. School of Aerospace Engineering Universiti Sains Malaysia Nibong Tebal 14300 Pulau Pinang. Bugs in code. There are three types of bugs (errors)

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EMT 101 – Engineering Programming

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  1. Week 2 EMT 101 – Engineering Programming Dr. Farzad Ismail School of Aerospace Engineering UniversitiSains Malaysia NibongTebal 14300 Pulau Pinang

  2. Bugs in code • There are three types of bugs (errors) • Syntax errors – violation of the grammatical rules of the programming language • A compiler would detect syntax errors. • Semantic errors – violation of the ‘meaning’ or ‘action’ of the code – compiler does NOT detect and the code can run • Algorithm errors – most difficult to be detected

  3. Example: Syntax Error • int main () { cout << “Hello world << endl; return 0; } Syntax Error: undeclared identifier “cout” Line 4 of program 1stprog.cpp

  4. Example: Syntax Error include <math> • int main () { int num; float value; double bigNum; bignum = num + value; } Can you detect the error?

  5. Example: Semantic Error • char response; cout << “Please input (y)es or (n)o: ” << endl; cin >> response; while ( (response != ‘y’) || (response!= ‘n’) ) { cout << “Please try again. Enter (y)es or (n)o: ” << endl; } The expression for while is always true regardless of what input you enter!

  6. Discussion on semantic error example(Boolean Algebra) • If user enters ‘y’, the first part of the expression is false but the second part is true -> overall true due to OR. • If user enters ‘n’, the first part is true but second part is false -> true • The program would keep on asking to try again regardless (infinite loop!) • Corrected by (response != ‘y’) && (response!= ‘n’)

  7. Example: Dangling if-else • if (condition 1) if (condition 2) cout << “output: ” << endl; else cout << “neither” << endl; Correct version: if (condition 1) { if (condition 2) cout << “output: ” << endl; } else cout << “neither” << endl;

  8. Example: Algorithm Error • Find TKE double TKE = 0.0; • for (inti=0; i < n, i++) { KE[i] = u[i]*v[i] + v[i]*u[i]; TKE += KE[i]; }

  9. Strategies to detect errors (bugs) • Trace by hand – trace each step of program execution by pen and paper to recreate the output -> ok for small programs but tedious for large complicated ones! • Program tracing – print out statements inserted in to programs at key locations to track the changing of variables to see how program is progressing, step-by-step. Can also used function calls and flags! • System interactive debugger – a software package that allows you to run your program in a step-by-step mode, automatically keeping track of all variables in code as it is executed.

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