Lecture 2: Introduction to C Programming

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.

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?

Definition of variable scanf obtains a value from the user and assigns it to integer1 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* indicate that program ended successfully */ } /* end function main */ Checked if integer1 is odd

Comments: Used to describe program #include : 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 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* 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 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* 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 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* 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 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* 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 /* Determine if a user-entered number is odd. */ #include /* 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 ); return 0; /* indicate that program ended successfully */ } /* end function main */

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 … … … integer1 integer2 sum RAM

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

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))

Some Arithmetic Operators

Equality and Relational Operators

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