weve What learned so far
Basic structure of a C program Printing output: printf Reading in input: scanf Basic arithmetic operations Decision making: if statements Debugging programs Algorithms Reading for this week Chap. 3 Section 4.10
Additional Options for printf / scanf
We used the following scanf and printf statements last week:
scanf( %d, &integer1 ); printf( Sum is %d\n\n, sum );
Here integer1 and sum were variables, and %d indicated the format of the data (we used %d for integer).
Other format types:
%d = decimal integer (can also be of the form %.3d, %5d or %5.3d) %f = floating point number (can also be of the form %.2f or %6.2f) %lf = double (use %f in printf statement, %lf in scanf statement) %c = character %s = string (in printf only)
Example Program
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 /* More on printf */ #include <stdio.h> /* function main begins program execution */ int main() { float pie = 3.1416; printf( "\n%.3d is an integer.", 15 );
printf( "\n%.3f is a floating point number.", pie ); printf( "\n%s is a string\n", "aabbbcc" ); return 0; /* indicate that program ended successfully */ } /* end function main */
Example Program Output
Output for program on previous page:
% a.out 015 is an integer. 3.142 is a floating point number. aabbbcc is a string. %
Flow chart for an if statement
if (num1 % 7 == 0 ) printf( %d is divisible by 7.\n, num1 );
true num1 % 7 == 0 print num1 is
false
The ifelse Selection Statement
if
Only performs an action if the condition is true
if...else
Specifies an action to be performed both when the condition is true and when it is false.
Pseudocode
If ( num1 mod 7 ) is equal to 0 Print num1 is divisible by 7 else Print num1 is not divisible by 7
Flow chart for an ifelse statement
if (num1 % 7 == 0 ) printf( %d is divisible by 7.\n, num1 ); else printf(%d is not divisible by 7.\n, num1 );
print num1 is not
false
true num1 % 7 == 0 print num1 is
The ifelse Selection Statement
C code:
if ( num1 % 7 == 0 ) { printf( %d is divisible by 7\n, num1 ); } else { printf( %d is not divisible by 7\n, num1 ); }
Ternary conditional operator (?:)
Takes 3 arguments
( condition ? value if true : value if false )
Examples:
printf( %s\n, grade >= 60 ? Passed : Failed ); grade >=60 ? printf( Passed\n ) : printf( Failed\n );
C Program: ifelse
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 /* decision making: using the if...else statement*/ #include <stdio.h> /* function main begins program execution */ int main() { int num1; /* declare variables */ printf( "\nEnter an integer, and I will tell you\n" ); printf( "if it is divisible by 7: " ); scanf( "%d", &num1 ); /* read integer */
if ( num1 % 7 == 0 ){ printf( "%d is divisible by 7.\n", num1 ); } else { printf( "%d is not divisible by 7.\n", num1 ); } return 0; /* indicate that program ended successfully */ } /* end function main */
C Program: nested ifelse
1 2 3 4 5 6 7 8 9 10 11 12 13 /* using nested if...else statements*/ #include <stdio.h> /* function main begins program execution */ int main() { int score; /* declare variables */ printf( "\nEnter your score, and I will tell you\n" ); printf( "your grade: " ); scanf( "%d", &score ); /* read integer */
C Program: nested ifelse
if ( score >= 90 ) 14 printf( "You got an A.\n" ); 15 else 16 if ( score >= 80 ) 17 printf( "You got a B.\n" ); 18 else 19 if ( score >= 70 ) 20 printf( "You got a C.\n" ); 21 else 22 if ( score >= 60 ) 23 printf( "You got a D.\n" ); 24 else 25 printf( "You got an F.\n" ); 26 27 return 0; /* indicate that program ended successfully */ 28 29 30 } /* end function main */
C Program: ternary conditional operator
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 /* using the ternary conditional operator */ #include <stdio.h> /* function main begins program execution */ int main() { int score; /* declare variables */ printf( "\nEnter your score, and I will tell you\n" ); printf( "if you passed: " ); scanf( "%d", &score ); /* read integer */
printf( "%s\n", score >= 60 ? "You passed!!!" : "You failed." ); return 0; /* indicate that program ended successfully */ } /* end function main */
Logical Operators
&& ( logical AND )
Returns true if both conditions are true
|| ( logical OR )
Returns true if either of its conditions are true
! ( logical NOT, also called logical negation )
Reverses the truth/falsity of a statement
Example Program
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 /* logical operators, using the ternary conditional operator */ #include <stdio.h> int main() { int num1, num2, num3, num4; printf( "\nEnter two integers, and I will tell you\n" ); printf( "if they are both even: " ); scanf( "%d%d", &num1, &num2 ); /* read integer */
/* check if both integers are even */ num1 % 2 == 0 && num2 % 2 == 0 ? printf( "\nBoth integers are even.\n\n" ) : printf( "\nAt least one integer is not even.\n\n" );
Example Program
19 20 21 22 23 24 25 26 27 28 29 30 31 32 printf( "\nEnter two integers, and I will tell you\n" ); printf( "if at least one is even: " ); /* check if at least one integer is even */ scanf( "%d%d", &num3, &num4 ); /* read integer */
num3 % 2 == 0 || num4 % 2 == 0 ? printf( "\nAt least one integer is even.\n\n" ) : printf( "\nNeither integer is even.\n\n" ); return 0; /* indicate that program ended successfully */ } /* end function main */
Example Program with Logical NOT
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 /* example with logical NOT */ #include <stdio.h> /* function main begins program execution */ int main() { int num1; /* declare variables */ printf( "\nEnter a positive integer, and I will tell you\n" ); printf( "if it is divisible by 7: " ); scanf( "%d", &num1 ); /* read integer */
if ( !( num1 > 0) ) printf( "\nThe integer you entered is not positive.\n" ); else printf( "\n%d is%sdivisible by 7.\n", num1, num1 % 7 == 0 ? " " : " not " ); return 0; /* indicate that program ended successfully */ } /* end function main */
The while Repetition Statement
Repetition statement
Programmer specifies that an action is to be repeated while some condition remains true
while statement
Pseudocode While there are more items on my shopping list, Purchase next item and cross it off my list. while loop repeated until condition becomes false
The while Repetition Statement
Example
int product = 1; while ( product < 1000 ) { printf( %d\n, product ); product 2 = * product; }
product < 1000
true
print product; product = 2*product;
false
Formulating program with a while loop
Program with a while loop (and many other programs as well) have 3 phases:
Initialization: define and initialize program variables Processing: input data values and perform all processing of data Termination: Calculate and print final results
Counter-Controlled Repetition
Counter-controlled repetition
Loop repeated until counter reaches a certain value Example: A class of n students took a quiz. The grades for this quiz are available to you. Determine the class average on the quiz. Pseudocode Set total to zero. Set counter to one. User inputs number of students in class. While counter is less than or equal to number of students, Input the next grade. Add the grade to the total. Add one to the grade counter. Set average to the total divided by the number of students. Print the class average.
Ex. Prog. Counter-controlled repetition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 /* class average program with counter-controlled repetition */ #include <stdio.h> int main() { /* define variables */ int students; /* number of students in the class */ int counter; /* grade number to be entered */ int grade; /* grade value */ float total; /* sum of all grades that have been input */ float average; /* average of grades */ /* initialize variables */ total = 0; /* initialize total */ counter = 1; /* initialize loop counter */ /* initialize students */ printf( "\nEnter the total number of students in the class: " ); scanf( "%d", &students );
Ex. Prog. Counter-controlled repetition
20 /* process while loop */ 21 while ( counter <= students ) { /* set up loop */ 22 printf( "Enter grade %d: ", counter ); /* ask for input */ 23 scanf( "%d", &grade ); /* read grade from user */ 24 total = total + grade; /* add grade to total */ 25 counter = counter + 1; /* increment counter */ 26 } /* end while */ 27 28 /* perform calculations */ 29 average = total / students; 30 31 /* display results */ 32 printf( "The class average is %.2f.\n\n", average ); 33 34 return 0; 35 36 37 } /* end function main */
Program Output
% a.out Enter the total number of students in the class: 4 Enter grade 1: 56 Enter grade 2: 68 Enter grade 3: 98 Enter grade 4: 47 The class average is 67.25. %
Prog. 2 Counter-controlled repetition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 /* example of a while repetition statement*/ #include <stdio.h> int main() { /* convert 10 angles from degrees to radians */ /* initialize variables */ int counter = 1; float angle; /* process while loop */ while ( counter <= 10 ) { printf( "Enter angle %d in degrees: ", counter ); scanf( "%f", &angle ); printf( "Angle %d in radians is %.2f.\n", counter, angle*3.1416/180); counter = counter + 1; } return 0; } /* end function main */
Sentinel-Controlled Repetition
Sentinel-controlled repetition
Loop repeated until user enters a sentinel value (also called a flag value) Flag value indicates end of data entry End loop when user enters flag value Flag value chosen so that it cannot be confused with a regular input (such as -1 in the following example) Example: A class of students took a quiz. The grades for this quiz are available to you. Determine the class average on the quiz.
Sentinel-Controlled Repetition
Pseudocode Set total to zero and counter to zero. Input the first grade (possibly the flag value). While grade not equal to sentinel, Add the grade to the total. Add 1 to counter Input the next grade (possibly the flag value). If counter is not equal to zero, Set average to the total divided by the counter. Print the average. Else Print No grades were entered.
Ex. Prog. Sentinel-controlled repetition
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 /* class average program with sentinel-controlled repetition */ #include <stdio.h> int main() { /* define and initialize variables */ int counter = 0; /* grade number to be entered */ int grade; /* grade value */ float total = 0; /* sum of all grades that have been input */ float average; /* average of grades */
/* get first grade from user */ printf( "\nEnter grade (enter -1 to end): " ); scanf( "%d", &grade );
Ex. Prog. Sentinel-controlled repetition
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 /* process while loop */ while ( grade != -1 ) { /* set up loop */ total = total + grade; /* add grade to total */ counter = counter + 1; /* increment counter */ printf( "Enter grade (enter -1 to end): " ); scanf( "%d", &grade ); } /* end while */ /* termination phase */ if (counter != 0 ) { average = total / counter; printf( "The class average is %.2f.\n\n", average ); } /* end if */ else /* if no grades were entered, output message */ printf( "No grades were entered.\n\n" );
return 0; } /* end function main */
Program Output
% a.out Enter grade (enter -1 to end): Enter grade (enter -1 to end): Enter grade (enter -1 to end): Enter grade (enter -1 to end): Enter grade (enter -1 to end): The class average is 67.25. % % a.out Enter grade (enter -1 to end): -1 No grades were entered. % 56 68 98 47 -1
Nested Control Structures - Example
Problem
A college has a list of test results (1 = pass, 2 = fail) for 10 students Write a program that allows the user to enter each students results and then prints how many passed and how many failed
Output should look like:
% a.out Enter result Enter result Enter result Enter result Enter result Enter result Enter result Enter result Enter result Enter result Passed: 6 Failed: 4 %
(1=pass, (1=pass, (1=pass, (1=pass, (1=pass, (1=pass, (1=pass, (1=pass, (1=pass, (1=pass,
2=fail): 2=fail): 2=fail): 2=fail): 2=fail): 2=fail): 2=fail): 2=fail): 2=fail): 2=fail):
1 2 2 1 1 1 2 1 1 2
Ex. Prog. Nested control structures
1 2 3 4 5 6 7 8 9 10 11 /* example with nested control structures: exam results */ #include <stdio.h> int main() { /* define and initialize variables */ int passes = 0; /* number of passes */ int failures = 0; /* number of failures */ int student = 1; /* student counter */ int result; /* one exam result */
Ex. Prog. Nested control structures
12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 /* process 10 students using counter-controlled loop */ while ( student <= 10 ) { /* set up loop */ printf( "Enter result (1=pass, 2=fail): "); scanf( "%d", &result ); /* if result = 1, increment passes. else, increment failures */ if ( result == 1 ) passes = passes + 1; else failures = failures + 1; student = student + 1; } /* end while */ /* display number of passes and failures */ printf( "Passed: %d\n", passes ); printf( "Failed: %d\n\n", failures ); return 0; } /* end function main */