C Fundamentals

Declarations, Identifiers & Statements

The // style command was added in C99

Normally all declarations are supposed to be at the start of the function
In C99 support to have declarations after statements were added

float fahrenheit; // Declaration
 
printf("Enter temperature (in fahrenheit): ");
scanf("%f", &fahrenheit);
 
float celsius; // Declaration (Would be invalid in ASNI C)
celsius = (fahrenheit - FREEZING_PT) * SCALE_FACTOR;

The names used to create variables, functions and other entities are called identifiers

Input & Output

#include <stdio.h>
 
#define FREEZING_PT 32.0f
#define SCALE_FACTOR (5.0f / 9.0f)
 
int main(void) {
    float fahrenheit, celsius;
    
    printf("Enter temperature (in fahrenheit): ");
    scanf("%f", &fahrenheit);
 
    celsius = (fahrenheit - FREEZING_PT) * SCALE_FACTOR;
    printf("Temperate (in celsius): %.2f\n", celsius);
 
    return 0;
}

The F in printf and scanf stands for formatted
These functions require a format string to specify the type of data to input and output

printf Function

C compilers are not required to check if the number of conversion specifiers in a format string watches the number of output items.

printf("%d %d\n", i); /*** WRONG ***/
printf("%d\n", i, j); /*** WRONG ***/
printf("%f %d\n", i, x); /*** WRONG ***/

Conversion Specification

The characters that start with % are called conversion specification
Conversion specifications define how to convert the internal form (binary) of data into its printed form (characters)

General Form: %m.pX or -%m.pX
m and p are integers and X is a letter (conversion specification)
m and p are optional. If p is dropped, the decimal point is also dropped

Minimum field width (m) specifies how many characters should be printed
If the number is shorter than the width the output is right justified with space as padding

The - sign is used to left justify the string
p when used with an integer controls the number of digits that will be shown. If the number is smaller than p it will be padded with zeros.

i = 40;
printf("|%5.3d|\n", i);
//|  040|

%e: Float in Exponential Form
%f: Flat in Fixed decimal form
%g: Float in exponential or fixed-decimal form based on size

scanf Function

scanf is essentially a “pattern-matching” function that tries to match up groups of input characters with conversion specifications
When providing input the values can be separated by spaces, new lines and tabs

int i, j;
float x, y;
scanf("%d%d%f%f", &i, &j, &x, &y);

Integers: Searches for digital, plus or minus sign and reads until it reaches a non-digit
Float: Searches for plus or minus sign (optional) followed by a series of digits (possibly containing a period) followed by an exponent (optional). Exponents consist of e or E followed by a plus or minus sign (optional) and one or more digits.

The call to scanf can contain ordinary characters. It will pattern-match the ordinary characters in the format string with the ordinary characters that are provided in the input.

%d: Base-10 number
%i: Base-8, Base-10 or Base-16 number

scanf has a return value which equals to the numbers of inputs it was able to read