cisc1110 fall 2010 lecture VI.2 call by value function parameters another call by value example:

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1 cisc1110 fll 2010 lecture VI.2 cll y vlue function prmeters more on functions more on cll y vlue nd cll y reference pssing strings to functions returning strings from functions vrile scope glol vriles nother cll y vlue exmple: int dd( int, int ); // prototype int p =, q =, sum; sum = dd( p, q ); ret = + ; // end of dd() cisc1110-fll2010-sklr-lecvi.2 1 cisc1110-fll2010-sklr-lecvi.2 2 cll y vlue prmeters: exmple with nnottions int dd( int, int ); int p=, q=, sum; sum = dd( p, q ); ret = + ; // end of dd() function rguments: the vlues of p nd q re used to initilize the vlues of the prmeters (,) inside the function function return: the vlue of "sum" is ssigned to the function s return vlue vlue prmeters: the initil vlues of nd re set sed on the vlues of the rguments used to cll the function return vlue: the vlue of "ret" is returned y the function to the cller cll y vlue prmeters: sme exmple s ove, ut using shorthnd int dd( int, int ); // prototype cout << "sum=" << dd(, ) << endl; P q sum ret return( + ); // end of dd() the rguments in min() re constnts (, ), which re used to initilize the vriles ( nd ) inside the function dd() cisc1110-fll2010-sklr-lecvi.2 3 cisc1110-fll2010-sklr-lecvi.2 4

2 nother cll y reference exmple: cll y reference function prmeters int dd( int, int, int & ); // prototype void dd( int, int, int &sum ) { sum = + ; // end of dd() exmple with nnottions: void dd( int, int, int & ); int p=, q=, sum; dd( p, q, sum ); function rguments: the vlues of p nd q re used to initilize the vlues of the prmeters (,) inside the function; the vlue of sum is chnged inside the function cll nd, ecuse it is reference prmeter, the new vlue is retined when the function exits nd ssigned to the vlue of the rgument in min() vlue prmeters: the initil vlues of nd re set sed on the vlues of the rguments used to cll the function void dd( int, int, int &sum ) { sum = + ; // end of dd() reference prmeter: the vlue of "sum" is chnged oth inside the function nd within the scope of the cller int p =, q =, sum; dd( p, q, sum ); P q sum sum cisc1110-fll2010-sklr-lecvi.2 cisc1110-fll2010-sklr-lecvi.2 6 multiple function prmeters clssic exmple, swp, which uses reference prmeters you cn write functions tht hve more thn one prmeter the prmeters cn e of ny dt type; they cn even e different dt types exmple: int domth( int A, int B, chr op ) { int result; if ( op== + ) { result = A + B; else if ( op== - ) { result = A - B; else if ( op== * ) { result = A * B; else { result = -999; return result; // end of domth() void swp( int &, int & ); // prototype int p =, q = ; swp( p, q ); void swp( int &, int & ) { int tmp; // end of swp() cisc1110-fll2010-sklr-lecvi.2 cisc1110-fll2010-sklr-lecvi.2 8

3 compre with noswp, which uses vlue prmeters pssing C++ strings to functions void noswp( int, int ); // prototype int p =, q = ; noswp( p, q ); void noswp( int, int ) { int tmp; // end of noswp() you pss C++ strings to functions in the sme wy tht you pss primitive vriles exmple cll y vlue string prmeters: void noswp( string, string ); // prototype string p = "hello", q = "goodye"; noswp( p, q ); void noswp( string, string ) { string tmp; // end of noswp() cisc1110-fll2010-sklr-lecvi.2 9 cisc1110-fll2010-sklr-lecvi.2 10 exmple cll y reference string prmeters: void swp( string &, string & ); // prototype string p = "hello", q = "goodye"; swp( p, q ); void swp( string &, string & ) { string tmp; // end of swp() cisc1110-fll2010-sklr-lecvi.2 11 returning strings from functions you return C++ strings from functions in the sme wy tht you return primitive vriles exmple: string getmove( chr ); // function prototype cout << "C = " << getmove( C ) << endl; cout << "D = " << getmove( D ) << endl; string getmove( chr move ) { switch( move ) { cse C : return "cooperte"; rek; cse D : return "defect"; rek; return " "; // end of getmove() cisc1110-fll2010-sklr-lecvi.2

4 pssing C strings is more complicted pssing C strings to functions this is ecuse C strings re lwys reference prmeters (hs to do with how they re stored) so just e creful if you pss C strings s prmeters nd know tht if their vlue will chnges inside the function, the new vlue will e retined outside here s n exmple: #include <cstring> #include <cctype> int countvowels( chr [] ); void trnsform( chr [] ); chr mystring[] = "hello"; cout << "mystring = [" << mystring << "] "; cout << "numer of vowels = " << countvowels( mystring ) << endl; cisc1110-fll2010-sklr-lecvi.2 13 cout << "efore trnsform: [" << mystring << "]\n"; trnsform( mystring ); cout << "fter trnsform: [" << mystring << "]\n"; int countvowels( chr [] ) { int sum = 0; for ( int i=0; i<strlen(); i++ ) { if (( [i] == A ) ( [i] == ) ( [i] == E ) ( [i] == e ) ( [i] == I ) ( [i] == i ) ( [i] == O ) ( [i] == o ) ( [i] == U ) ( [i] == u )) { sum++; return( sum ); // end of countvowels() void trnsform( chr [] ) { for ( int i=0; i<strlen(); i++ ) { [i] = toupper( [i] ); // end of trnsform() cisc1110-fll2010-sklr-lecvi.2 14 Note tht you cn return C strings from functions, ut it is more complicted nd involves syntx nd concepts tht re eyond the scope of this clss You will likely cover tht in the next course (CISC 3110) So, if you wnt function to return string, then use C++ strings vrile scope vriles re defined within either glol or locl scope locl vriles re defined inside function nd these go wy when the function exits glol vriles re defined outside of ny function, nd these do not go wy (s long s the progrm is running) in the exmple elow: nd re locl vriles declred inside dd(); their scope is the function dd(); when dd() exits, nd no longer exist p nd q re locl vriles declred inside min(); their scope is the function min(); they lso go wy when min() exits, which is the sme thing s when the progrm exits, ecuse min() is the specil function tht controls the progrm cisc1110-fll2010-sklr-lecvi.2 1 cisc1110-fll2010-sklr-lecvi.2 16

5 glol vriles exmple exmple similr to those ove, except using glol vriles int dd( int, int ); // prototype int p =, q = ; // declre glol vriles exmple with nnottions: int dd( int, int ); int p=, q=; return( + ); // end of dd() glol vriles function rguments cout << "sum=" << dd( p, q ) << endl; function cll nd return vlue prmeters return vlue cout << "sum=" << dd( p, q ) << endl; ret = + ; // end of dd() glol: P q dd(p,q) ret cisc1110-fll2010-sklr-lecvi.2 1 cisc1110-fll2010-sklr-lecvi.2 18