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Understanding Variable Declarations and Input/Output in C Programming

This lecture series provides a comprehensive overview of variable declarations in C, including value-oriented and address-oriented approaches. It covers fundamental concepts like variable attributes, memory mapping, and function prototypes, elaborating on how parameters can either require values or addresses. Additionally, the notes explain the usage of `scanf` and `printf` for user input and output, emphasizing the importance of correct placeholder usage and the need to manage buffer flushing for character inputs. Gain insights into variable management and data handling in C programming.

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Understanding Variable Declarations and Input/Output in C Programming

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  1. Engr 0012 (04-1) LecNotes 19-01

  2. address (where located in computer) type of information value C assigns this programmer assigns this user or programmer assigns this Variable (data object) declaration in C variable attributes Engr 0012 (04-1) LecNotes 19-02

  3. Variable (data object) declaration in C types of variables Engr 0012 (04-1) LecNotes 19-03

  4. Value-oriented Address-oriented int a; int *pa; 0065FDF4 0065FE4D a 154 pa 0065FDF4 int int address Variable (data object) declaration in C two methods of variable declaration address address name name type type a ==> value (154) pa ==> address (0065FDF4) &pa ==> address (0065FE4D) &a ==> address (0065FDF4) *pa ==> value (154) Engr 0012 (04-1) LecNotes 19-04

  5. seen in prototype parameter list seen in variable declaration section Variable (data object) declaration in C value-oriented declarations int myfunction( int i1, double d1 ) // myfunction description { //begin myfunction // variable declaration int i2,i3; // two ints double d2,d3; // two doubles char c1; // a character // algorithm … } //end myfunction most common declaration - emphasizes value Engr 0012 (04-1) LecNotes 19-05

  6. sets up memory map on scrap paper &i1 &d1 &i2 &i3 &d2 &d3 &c1_ 43.2 ?? ?? ?? ?? ?? where did these values come from? Variable (data object) declaration in C value-oriented declarations int myfunction( int i1, double d1 ) // myfunction description { //begin myfunction // variable declaration int i2,i3; // two ints double d2,d3; // two doubles char c1; // a character // algorithm … } //end myfunction Engr 0012 (04-1) LecNotes 19-06

  7. seen in prototype parameter list Variable (data object) declaration in C address-oriented declarations void myfnc2( int i1, int *pi2, int *pi3 ) // myfnc2 description { //begin myfunction // variable declaration int i4,i5; // two ints double d1,d2; // two doubles char c1; // a character // algorithm … } //end myfunction used when we want to share an address between functions Engr 0012 (04-1) LecNotes 19-07

  8. contents are addresses! sets up memory map on scrap paper &i1 &pi2 &pi3 &i4 &d1 &c1_ 462AE62AF ?? ?? ?? where do these come from? Variable (data object) declaration in C address-oriented declarations void myfnc2( int i1, int *pi2, int *pi3 ) // myfnc2 description { //begin myfunction // variable declaration int i4; // an int double d1; // a double char c1; // a character // algorithm … } //end myfunction Engr 0012 (04-1) LecNotes 19-08

  9. function prototypes/calling statements value-oriented parameters require values address-oriented parameters require addresses double fcn1( int i1, double d1, int *pi2 ) possible calling statements a = fcn1( 1, 3.2, &myint ); q = fcn1( alpha, beta, &thisint ); w = fcn1( alpha, cos(beta), &anyint ); Engr 0012 (04-1) LecNotes 19-09

  10. getting information from keyboard: scanf scanf requires two things type of value expected - denoted by placeholder where to store value - address of variable printf( “\nPlease enter an integer ==> ”); scanf( “%d”, &i1 ); need to printf before scanf printf( “\nPlease enter a real number ==> ”); scanf( “%lf”, &d1 ); caution - always flush keyboard buffer before & after char input printf( “\nPlease enter a character ==> ”); fflush( stdin ); scanf( “%c”, &c1 ); fflush( stdin ); Engr 0012 (04-1) LecNotes 19-10

  11. displaying information to screen: printf printf requires a control string that tells what to display values to display are optional!!! printf( “\nPlease enter an integer ==> ”); to display values, insert placeholders in control string & list values (in order) after control string printf( “\nCircle of radius %.4lf has area %.4lf”, 1, 3.14159 ); printf( “\nCircle of radius %.4lf has area %.4lf”, radius, circ_area ); Engr 0012 (04-1) LecNotes 19-11

  12. scanf simply enclose placeholder “%d” in double quotes printf can format output display w is a number that tells how many spaces to use %wd w tells how many (total) spaces to use %w.plf p tells how many decimal places to use le: (long) scientific notation display %w.ple placeholders Engr 0012 (04-1) LecNotes 19-12

  13. is the same as a=6.3; is the same as a = 6.3; no comma! general notes on C C ignores whitespace - semicolons terminate statements a = 6.3; printf( “\nCircle of radius %.4lf has area %.4lf”, radius, circ_area ); to break a control string for easy reading in the text editor printf( “\nCircle of radius ” “%.4lf has area %.4lf”, radius, circ_area ); Engr 0012 (04-1) LecNotes 19-13

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