Relational operators (1)

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1 Review-2 Control of flow: ifs & loops How to set them up Where to break to When to use which kind Introduction to C-Programming 10-1 Relational operators (1) Relational Operators <= less or equal than < less than >= greater or equal than > greater than!= not equal == equal Example: if x=3 and y=33 the expression x == y is the expression x < y is the expression x+y>50 is Results: True or False Introduction to C-Programming

2 Relational operators (2) C does not have a special data type to represent true and false. Instead, false is represented by the value 0, and true is represented by any value other than 0. Any arithmetic expression different that 0 can be used as a logical value true Given: x= 1, y=4, z= 6 x < z+y y == 2*x x!= y x Introduction to C-Programming 10-3 Control of flow-rational operator Testing true/false of a set of conditions Return T or F often followed by actions Can use ( ) if you want e.g. if temp>85 turn on AC if temp<65 turn on heater if ( (g==female) && (major==eng) ) print name if (account_bal<0) print a letter Introduction to C-Programming

3 Decision making if- Test condition(s), action(s) to follow Single alternative, if Double alternatives: if- More than two alternatives: if- if No end if Long actions, use Introduction to C-Programming 10-5 Decision making: switch and nested if Switch have to know all possible value (not range) of expression before hand. e.g. section 51, 52 or 53 sometime clear than if- if be careful when to break Nested if have a flowchart WILL help use indentation/different color in the code if ( ),, if ( ), switch all part of a block, thus no ; after Introduction to C-Programming

4 Example: input age from keyboard, group into very young (<25), young (25 to 45), still young (45-65), and young in heart (65 and up). One condition (age) Four outcomes, each do group =i, i=1..4 If If- If- if Case Nested-if Loops Introduction to C-Programming 10-7 int age, group=0; printf ("\n INPUT age, positive integer only: \n"); int age, group=0; printf ("\n INPUT age, positive integer only: \n"); if ( age< 25) group =1; if ( age<45) group =2; if ( age<65) group =3; group =4; printf(" \n age group 1, 2,3, or 4: %d", group); if ( age< 25) group =1; if ( age< 45) group =2; if ( age< 65) group =3; if ( age>=65) group =4; printf(" \n age group 1, 2,3, or 4: %d", group); Introduction to C-Programming

5 int age, group=0; printf ("\n INPUT age, positive integer only: \n"); if ( age< 25) group=1; if ( age>= 25 && age< 45) group=2; if (age>= 45 && age< 65) group=3; if ( age>65) group=4; printf(" \n age group 1, 2,3, or 4: %d", group); int age, group=0; printf ("\n INPUT age, positive integer only: \n"); if ( age< 25) group =1; if ( age< 45) group =2; if ( age< 65) group =3; if ( age>=65) group =4; printf(" \n age group 1, 2,3, or 4: %d", group); Introduction to C-Programming 10-9 Example: input age from keyboard, group into very young (<25), young (25 to 45), still young (45-65), and young in heart (65 and up). When input 0, stop int age, sum1=0, group=0; printf ("\n INPUT age, positive integer only: \n"); if ( age!= 0 ) if ( age< 25) group=1; if ( age<45) group=2; if ( age<65) group=3; group=4; printf(" \n age group 1, 2,3, or 4: %d", group); Introduction to C-Programming

6 Example: input age from keyboard, group into very young (<25), young (25 to 45), still young (45-65), and young in heart (65 and up). Repeat, when input 0, print number of people in each group, and stop int age, sum1=0, sum2=0, sum3=0, sum4=0; input: printf ("\n INPUT age, positive integer only: \n"); if ( age!= 0 ) if ( age< 25) sum1=sum1+1; if ( age<45) sum2=sum2+1; if ( age<65) sum3=sum3+1; sum4=sum4+1; // goto input printf(" \n no of people in group 1, 2,3, and 4, %d, %d,%d, %d, sum1, sum2, sum3, sum4); Introduction to C-Programming Example: input age from keyboard, group into very young (<25), young (25 to 45), still young (45-65), and young in heart (65 and up). Repeat, when input 0, print number of people in each group, and stop. Use while int age, sum1=0, sum2=0, sum3=0, sum4=0; printf ("\n INPUT age, positive integer only, zero to stop: \n"); while (age!=0) if ( age< 25) sum1=sum1+1; if ( age<45) sum2=sum2+1; if ( age<65) sum3=sum3+1; sum4=sum4+1; printf ("\n INPUT age, positive integer only: \n"); printf(" \n no of people in group 1, 2,3, and 4: %d, %d,%d, %d, sum1, sum2, sum3, sum4); Introduction to C-Programming

7 int age, sum1=0, sum2=0, sum3=0, sum4=0; printf ("\n INPUT age, positive integer only, zero to stop: \n"); do if ( age< 25) sum1=sum1+1; if ( age<45) sum2=sum2+1; if ( age<65) sum3=sum3+1; sum4=sum4+1; printf ("\n INPUT age, positive integer only, zero to stop : \n"); while (age!=0); do loop printf(" \n no of people in group 1, 2,3, and 4, %d, %d,%d, %d, sum1, sum2, sum3, sum4); Introduction to C-Programming for loop int i, age, sum1=0, sum2=0, sum3=0, sum4=0; for (i=1; i<10000; i++) // a number >no. of record printf ("\n INPUT age, positive integer only, zero to stop: \n"); if (age==0) break; //or if (!age) break; if ( age< 25) sum1=sum1+1; if ( age<45) sum2=sum2+1; if ( age<65) sum3=sum3+1; sum4=sum4+1; // end of for loop printf(" \n no of people in group 1, 2,3, and 4, %d, %d,%d, %d, sum1, sum2, sum3, sum4); Introduction to C-Programming

8 int age, sum1=0, sum2=0, sum3=0, sum4=0; for ( ; ; ) // a dead loop, have to break somehow printf ("\n INPUT age, positive integer only: \n"); for loop if (age==0) break; //or if (EOF) break; if ( age< 25) sum1=sum1+1; if ( age<45) sum2=sum2+1; if ( age<65) sum3=sum3+1; sum4=sum4+1; int i, age, sum1=0, sum2=0, sum3=0, sum4=0; for (i=1; i<10000; i++) printf(" \n no of people in group 1, 2,3, and 4: %d, %d,%d, %d, sum1, sum2, sum3, sum4); 15 Summary: follow control Test condition(s), action(s) to follow if, if-, if- if : no. of alternative Test more then one condition, nested-if Known values (integer and char only), case Repeat: loops while (test first) do-while (do then test) for (more suitable for known number of repeats) Introduction to C-Programming

9 Summary: follow control use, flowchart, indentation, color to help Set up loops Initialization: e.g. sum=0; p=1; before the loop When to start: for (i=1;,,,) When to end: for (i=1; i<100;..), while (i<100) How to get from start to end: Known No. of repeated action: i++, --j inside or out for (), Unknown, e.g. read data from keyboard or files, EOF or a unique number: e.g for age Introduction to C-Programming Summary: follow control What should be in the loop? Inch feet meter End of table In - many times: each conversion, each income and tax Out - once: before or after the loop, header, footer, final result (8!) Introduction to C-Programming

10 Summary: follow control where to break (quit) to If: end of block Loops: 1 st command after the that pares with the right after do/while/for if ( ),, if ( ), switch, for, do, while all part of a block, thus no ; after them (note: while (age!=0); ) /* in addition to flowchart, indentation, color, blank line */ //good practice to mark end of if block, end of i loop Introduction to C-Programming Summary: more about loops control the loop (when to get out) By number for (i=1; i<10; i++) while (i<10) i is a counter By a flag: -999 as age, EOF ( end of file) use the counter or not Use the counter n!, key is find the pattern and associate it with the counter not use the counter: e.g. income fax Introduction to C-Programming

11 Your tasks Do your own review Print out Lecture 11&12 and preview Do assignment in the lab Introduction to C-Programming

Lesson #4. Logical Operators and Selection Statements. 4. Logical Operators and Selection Statements - Copyright Denis Hamelin - Ryerson University

Lesson #4. Logical Operators and Selection Statements. 4. Logical Operators and Selection Statements - Copyright Denis Hamelin - Ryerson University Lesson #4 Logical Operators and Selection Statements Control Structures Control structures combine individual instructions into a single logical unit with one entry point at the top and one exit point