CIS 15 NOTES - City University of New York
Review of C
Before a C program is compiled, it is first edited by a preprocessor. Commands intended for the preprocessor are called directives.
#include
This directive states that the information in is to be “included” into the program before it is compiled. contains information about C’s standard input/output library. C has a number of headers like . C has no built-in “read” and “write” commands, so we include . i/o is provided by the functions in the standard library. (scanf/printf).
Constants – values that don’t change during execution.
#define TRUE 1
#define FALSE 0
Selection, Iteration, Jump Statements
Selection statements – The if and switch statements allow a program to select a particular execution path from a set of alternatives
I. Selection Constructs
• if
• if/else
• nested if
• switch/case
if statement
In pseudocode (structured English) we might express a decision as:
If student’s grade is greater than or equal to 60
Print “Passed”
if (grade >= 60)
printf(“Passed”);
Syntax for if statement:
if ;
A boolean expression represents a condition that is either true or false. It is formed using operands (constants, variables) and operators (arithmetic operators, relational operators, logical operators).
|Arithmetic |
|+ - |
|* / % |
|arithmetic functions |
|Relational |
|< less than > greater than |
|== equal to |
|!= not equal to |
|= greater than or equal to |
|Logical |
||| or |
|&& and |
|! not |
Ex. if ((x > 0) && (a == b)) …
Operator Precedence
|Operator |Associativity |Type |
|( ) |L ( R |parenthesis |
| ++ – – + – ! |R ( L |unary operators |
|* ? % |L ( R |multiplicative |
|+ – |L ( R |additive |
|> |L ( R |insertion |
|< >= |L ( R |relational |
|= = != |L ( R |equality |
|&& |L ( R |and |
||| |L ( R |or |
|?: |R ( L |conditional |
|= += –= *= /= %= |R ( L |assignment |
if/else statement
In pseudocode:
If student’s grade is greater than or equal to 60
Print “Passed”
else
Print “Failed”
In C
if (grade >= 60)
printf(“Passed\n”);
else
printf(“Failed\n”);
55
Failed
syntax for if/else statement:
if [else ];
The C conditional operator - ?:
Same as the if/else structure but more compact. This is the only ternary operator in C. Example:
grade>=60? printf(“Passed”) : printf(“Failed”);
In this case, the conditional expression evaluates to “Passed” if the condition is true and to “Failed” if the condition is false.
Nested-if
/*nestedIf.c
This program converts a test score into
its equivalent letter grade. */
#include
int main()
{
int score;
printf("Enter the test score: ");
scanf(“%d”, &score);
if (score > 100) printf("Error: score is out of range.\n") ;
else if (score >= 90) printf(“A\n”);
else if (score >= 80) printf(“B\n”);
else if (score >= 70) printf(“C\n”);
else if (score >= 60) printf(“D\n”);
else if (score >= 0) printf(“F\n”);
else printf("Error: score is out of range.");
return 0; //successful termination
}
Enter the test score: 75
C
Switch
/*switch.c
This program converts a test score into
its equivalent letter grade, using a switch statement.*/
#include
int main()
{
int score;
printf("Enter the test score: ");
scanf(“%d”, &score);
switch (score/10) {
case 10:
case 9: printf(“A\n”); break;
case 8: printf(“B\n”); break;
case 7: printf(“C\n”); break;
case 6: printf(“D\n”); break;
case 5:
case 4:
case 3:
case 2:
case 1:
case 0: printf(“F\n”); break;
default: printf(“Error: score is out of range.\n");
}
return 0; //successful termination
}
Enter the test score: 83
B
II. Iteration Constructs
Iteration Statements – The while, do, and for statements support iteration (looping)
In order to control iteration, we use one of three structured control statements.
• for
• while
• do/while
A Counting Program: We would like to write a program that will print the integers between 1 and 20.
//counting2.c
// A Counting Program
// Using a FOR Loop
#include
int main()
{
int count ;
for (count=1; count ................
................
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