Lecture 2: Introduction to C Programming

1. Lecture 2: Introduction to C Programming

2. OBJECTIVES • In this lecture you will learn: • To use simple input and output statements. • The fundamental data types. • Computer memory concepts. • To use arithmetic operators. • The precedence of arithmetic operators. • To write simple decision-making statements.

3. Example • Problem: Determine if a user-entered number is odd. • Questions: • How to enter a number? • Where to store the number? • Under what condition is a number is odd?

4. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ Definition of variable scanf obtains a value from the user and assigns it to integer1 Checked if integer1 is odd

5. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ • Comments: Used to describe program • #include <stdio.h>: <stdio.h> allows standard input/output operations • int main() • C programs contain one or more functions, exactly one of which must be main • int means that main "returns" an integer value • The execution of any C program starts from main

6. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ • int integer1; • Definition of a variable: location in memory where a value can be stored. • int means the variable can hold an integer • Variable name (identifier) • integer1 • Identifier: consist of letters, digits (cannot begin with a digit) and underscores( _ ) • Case sensitive • Definitions appear before executable statements

7. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ • scanf( "%d", &integer1 ); • Obtains a value from the user -- uses standard input (usually keyboard) • Two arguments • %d - conversion specifier: data should be a decimal integer (“%d” is the format control string) • &integer1 - location in memory to store variable • When executing the program the user responds to the scanf statement by typing in a number, then pressing the enter (return) key

8. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ • if ( integer1 % 2 == 1 ) • printf( "The entered number %d is odd.\n", integer1 ); • Simple version of the if statement, more detail next lecture • If a condition is true, then the body of the if statement executed • 0 is false, non-zero is true. • Control always resumes after the if structure

9. /* Determine if a user-entered number is odd. */ #include <stdio.h> /* function main begins program execution */ int main( void ) { int integer1; /* the number to be input by user */ printf( "Enter an integer number:\n" ); /* prompt */ scanf( "%d", &integer1 ); /* read an integer */ /* determine if the number is odd using the modulus operator */ if ( integer1 % 2 == 1 ) printf( "The entered number %d is odd.\n", integer1 ); return0; /* indicate that program ended successfully */ } /* end function main */ • printf( "The entered number %d is odd.\n", integer1 ); • Similar to scanf • "The entered number %d is odd.\n” - printf format control string. • %d - conversion specifier: means decimal integer will be printed

10. Memory Concepts • Variable • Variable names correspond to locations in the computer's memory • Every variable has a name, a type, and a value • Whenever a new value is placed into a variable (through scanf, for example), it replaces (and destroys) the previous value • Reading variables from memory does not change them RAM … 2000 integer1 2500 sum … 500 integer2 …

11. Arithmetic • Arithmetic calculations • Use * for multiplication and / for division • Integer division truncates remainder e.g. 9 / 5 evaluates to 1. • Modulus operator (%) returns the remainder e.g. 9 % 5 evaluates to 4. • Operator precedence • Used to decide which of two operators should be processed first. • Parentheses () • Multiplication/Division/Remainder • Addition/Subtraction • Use parenthesis when needed • E.g.: Find the average of three variables a, b, and c using (a + b + c)/3, not a + b + c/3

12. Arithmetic • Operator associativity • used to decide which of two operators should be processed when both operators have same precedence. • Multiplication/Division: Left to Right • Addition/Subtraction: Left to Right • Examples: a - b + c = ((a - b) + c) a * b % c = ((a * b) % c) a^b^c = (a^(b^c))

13. Some Arithmetic Operators

14. Some Arithmetic Operators

15. Equality and Relational Operators

16. Keywords Special words reserved for C Cannot be used as identifiers or variable names