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C Language Notes

Other C notes:

Table of Contents

The main() Function

The main() function is the entry point of a C program.

int main(int argc, char **argv);
  • int argc: The number of command line arguments.
  • int **argv: The command line arguments as an array of strings.

Scoping

  • ->: Member access operator.
    • This is used for accessing members of a pointer.
  • .: Member access operator.
    • This is used for accessing members of a struct.

Typedef

Declaring a type alias and/or custom struct type is done with the typedef keyword. Example of a custom struct type: 

typedef struct this_is_optional {
    int num_needed;
    char **needed;
    // Or:
    /* int *needed[]; */

    int spent;
    /* int budget; */
} grocery_list_t;
Syntax broken down:

  • typedef struct this_is_optional:
    • This declares a struct type.
    • The this_is_optional is the name of the struct type.
      • This is optional, the actual name goes at the end of the block.
    • The struct members are defined inside the braces { }.
    • After the closing brace, we can define the name of the struct type.
      • In this case, grocery_list_t.
      • The _t is a naming convention for custom types.

Imports

Instead of #include <iostream> (C++), we can use #include <stdio.h> (C).

  • stdio.h is the library for IO (input/output).
  • stdlib.h is the library for memory (dynamic memory allocation).
  • string.h is the library that contains string functions.
  • assert.h is the library that contains the assert() function.

Printf Format Specifiers

For C programming: v_gF -> (man://printf(3))

Control Sequence Produces
\n newline
\l line-feed
\r return
\t tab
\b backspace
\f form-feed
\s space
\E and \e escape character
^x control-x (x=char)

Floats vs Doubles

Floats and Doubles both store floating point values.
Floats allow for 4 bytes (or 32 bits), while doubles are 8 bytes (or 64 bits).

Floats Doubles
4 bytes (32 bits) 8 bytes (64 bits)
7 decimal digits precision 15 decimal digits precision
possible precision errors with big numbers won't get precision errors with big numbers
Format specifier %f Format specifier %lf

Loops in C

int count = 10;
for (int i = 0; i < count; i++) {
    for (int j = 0; j < length; j++) {
        repeated_str[i + length + j]
    }
}

Compiling a C Program

To compile a C program, we need to use the gcc compiler. For example, to compile hello.c, we would run: 

gcc hello.c -o hello

  • gcc hello.c: This passes hello.c to the compiler.
  • -o: Tells gcc to output an executable binary named hello.