c tutorial - newcastle university...first example (using gcc) • example: ex_p1_1.c• read...

C Tutorial

Dr. Alex Bystrov

Newcastle University

School of Engineering

Induction week

Files, links

• See http://www.staff.ncl.ac.uk/a.bystrov/c_tutorial

• Uses the book ”C: How to Program” by Deitel

Why C?

• Small (32 keywords)

• Stable

• Existing code base

• Fast

• Low-level

Terminology

• Source code: (*.c) contain algorithms we are writing

• Header files: (*.h) interface to libraries

• Library: Collection of functions for specific tasks

• Compiler: translates source code to an executable

First Example (Using GCC)• Example: ex_p1_1.c

• Read c_tutorial.txt for the detailed instructions

• Create a directory ~/c_tutorial

• Inside this directory, create a file ex01.c using notepad++

• Type the code segment above

• Compile using: gcc ex01.c -o ex01

• Run the program:

• Don’t expect much as it does nothing !

main(){ }

1234

Example “Hello World!”

#include <stdio.h>

int main () { printf ("Hello world!\n");}

Third Example

• Example: ex_p1_3.c

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#include <stdio.h>

int main(void){

//Print somethingprintf("Hello World !\n");

//Require keyboard inputprintf("[Press any key to continue]\n");getchar();

//Exit to operating systemreturn 0;

}

Standard C Library

• Total of 24 libraries: (< > indicates system library)

• A few commonly used libraries:

• #include <math.h>

• #include <stdio.h>

• #include <stdlib.h>

• #include <time.h>

• #include <string.h>

Standard C Library (2)

• For other libraries:

Library is in current folder: #include "csp.h"

Library is in specific folder (Win): #include "H:\C_Tutorial\csp.h"

Library is in specific folder (Linux): #include "/home/ct/C_Tutorial/csp.h"

Comments• Single-line comments: //...

• Multi-line comments: /*... */


#include<stdio.h>/* This program prints hello world but also demonstrates the use of comments to add code explanations */int main(void){

// printf is included in stdio.hprintf("Hello World !\n");

//Require keyboard inputprintf("[Press any key to continue]\n");getchar();

return 0;}

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Variable Types

Qualifiers Modifiers Specifiers

char

int

float

double

void

const

volatile

short

long

signed

unsigned

Integer, Decimal Data Types

Memory Range Data Type 8 bit 0...255 unsigned char

16(32) bit 0...216(32)−1 unsigned int

32(64) bit 0...232(64)−1 unsigned long

8 bit −128...+127 signed char, char

16(32) bit −215(31)...+215(31)-1 signed int, int

32(64) bit −231(63)...+231(63)-1 long, long int

32 bit 1.17E-38...3.40E+38 float

64(128)bit 2.22E-308...1.79E+308 double

Variables and Constants

• All variables and constants should be declared first: ex_p1_5.c

// Global variables#define N 64 //integer constant #define PI 3.141592654 //floating point constantconst float pi = 3.141592654;#define SCALE (float) 1/32768 //derived constantfloat sample; //single precision floating pointdouble x = 0.0; //double precision floating pointint n; // signed integerunsigned count = 0; // unsigned integer, initialised

void main(void){

//local variablesint k, n;...

}

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Flow Control: if statement

• if syntax:

int m = 0, n = 0;... if (n > 10) n = 0;

if (n < 10){ n++; m--;}

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Flow Control: if, else• if-else syntax:

int m = 0, n = 0;... if (n > 10){ n = 0; m = 0;}else { n++; m++;}

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Flow Control: if, else if, else

• if, else if, else syntax:

int m = 0, n = 0;...if (m < 0) //Condition { n--; //n = n-1}else if (m > 0){ n++; //n = n+1}else{ n = 0;}

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Flow Control: Relational

• Relational less than/less than or equal to: <, <=

• Relational greater than/greater than or equal to: >, >=float x = 0.0, y = 0.0, z = 0.0;… //Code that modifies x,y,z valuesif (x >= y){ ... //Do something}else if (x <= z){ ... //Do something else}else... //Otherwise do this else

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Flow Control: Logical

• Logical EQUAL: ==

• Logical NOT: !=

int n; ... //Code that modifies the value of n if (n != 0) { ... //Do something }

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int n; ... //Code that modifies the value of n if (n == 0) { ... //Do something }

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Flow Control: Logical (2)

• Logical AND: &&

• Logical OR: | |

float x = 0.0, y = 0.0, z = 0.0;... //Code that modifies x,y,z valuesif ((x < y) && (y < z)){ ... //Do something}

float x = 0.0, y = 0.0, z = 0.0;... //Code that modifies x,y,z valuesif ((x >= y) || (y <= z)){ ... //Do something}

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Flow Control: case

unsigned day; ...//Code that modifies the value of dayswitch (day){ case 1: case 2: case 4: case 5: printf("Study hard\n"); break; case 3: printf("Study until 12:00am, go to gym\n"); break; case 6: case 7: printf("Relax\n"); break; default: printf("Study hard\n"); break; }

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I/O Functions: printf (1)

char ch = 'x';float pi=3.141592654;int m = 10; ...printf("The value of ch = %c \n", ch);printf("The value of pi = %f \n", pi);printf("The value of m = %d \n", m);

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• Placeholder anatomy: %[Modifier][Width][.Precision]Type

Spec Type Example%c char 'x'%d dec signed int -10%u dec unsigned int 131072%hu unsigned short int 2%f float, double 3.14 %e %E float exp. notation 3.14e0 or 3.14E0%x %X hex integer 0xff, 0xDEADBEEF%o octal integer 377%s string “hello!”


Modifier Description0 Pads the conversion on the left with zeroesnumber Pads the conversion on the left with spaces (right alignment)- The conversion is left aligned within the display width+ Forces to display a sign (+ or -)space Adds a space in front of positive numbers

Review Exercise 1

• Write a small program to compute the following:

• Solutions:

-0.5000, 0.3827, 1.0472, 1.0039

• Hint: include the <math.h> header and compile using:

gcc revex1.c -o revex1 -lm

cos(2π

3) ,sin( π

8) ,cos−1

(0.5), tan−1( π

2)

Review Exercise 2

• Write a small program to compute the roots of a

quadratic polynomial: ax2 + bx + c = 0

• Algorithm:Compute the discriminant

If D is positive, there are two real-valued roots:

If D is zero, there is a double real-valued root:

If D is negative, there are two complex-valued roots:

D=b2−4a c

x1=−b+√D

2a, x2=

−b−√D2a

x1=x2=−b2a

x1=−b2a

+ j √−D2a

, x2=−b2a

− j √−D2a

Review Exercise 2 (cont.)

• Hint: For the complex solution split it up into real and imaginary parts.

• Test your program with:

a = 2, b = −3 and c = 1.a = 1, b = −6 and c = 9.a = 2, b = −3 and c = 5.

Loops: for


• Compile using: gcc ex_p2_1.c -o ex_p2_1 -lmRun using: ./ex_p2_1 > data.txt

int n, N = 100;float fc = 1000.0; //Carrier frequency in Hzfloat fs = 48000.0; //Sampling frequencyfloat t, Ts, wc, xc;

Ts = 1.0 / fs; //Sampling timewc = 2.0 * M_PI * fc; //Generate cosine signalfor (n = 0; n < N; n++){

t = n * Ts;xc = cos(wc * t);printf("%+.7f, %+.7f\n", t, xc);

}

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Loops: while

• Example: ex_p2_2.c int n = 0, N = 100;float fc = 1000.0; //Carrier frequency in Hzfloat fs = 48000.0; //Sampling frequencyfloat t, Ts, wc, xc;

Ts = 1.0 / fs; //Sampling timewc = 2.0 * M_PI * fc;

//Generate cosine signalwhile(n < N){

t = n * Ts;xc = cos(wc * t);printf("%+.7f, %+.7f\n", t, xc);n++;

}

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Loops: do


int n = 0, N = 100;float fc = 1000.0; //Carrier frequency in Hzfloat fs = 48000.0; //Sampling frequencyfloat t, Ts, wc, xc;


//Generate cosine signaldo{

t = n * Ts;xc = cos(wc * t);printf("%+.7f, %+.7f\n", t, xc);

}while(++n < N);

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Structures: struct

• Definition 1:


struct cmplx x;

x.real = 1.0;x.imag = 1.0;printf("x = %+.3f %+.3f * j\n", x.real, x.imag);

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struct cmplx{ float real; float imag;}

Structures: struct, typedef

• Definition 2:


cmplx x;

x.real = 1.0;x.imag = 1.0;printf("x = %+.3f %+.3f * j\n", x.real, x.imag);

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typedef struct{ float real; float imag;} cmplx;

Arrays (1)

• Definitions: ex_p2_6.c

• Array index limits for an array with N elements:

Lower index limit: 0Upper index limit: N-1

float x[1000];float y[] = {1.0, 1.0, 1.0};float z[1000] = {0.0};int adc[1024];char text[] = "C is cool!";

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Arrays (2)


int n, N = 100;float fc = 1000.0; //Carrier frequency in Hzfloat fs = 48000.0; //Sampling frequencyfloat t, Ts, wc, xc[N];


//Generate cosine signalfor (n = 0; n < N; n++){

t = n * Ts;xc[n] = cosf(wc * t);printf("%+.7f, %+.7f\n", t, xc[n]);

}

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Two Dimensional Arrays


float X[3][3];float Y[3][3]={{1.0, 0.0, 0.0}, {0.0, 1.0, 0.0}, {0.0, 0.0, 1.0}};int m, n;

for (m = 0; m < 3; m++){

for (n = 0; n < 3; n++) printf("%f ",X[m][n] = 2.0 * Y[m][n]);printf("\n");

}

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Functions (1)

• Definition: ex_p2_9.c

typedef struct{

float real;float imag;float mag;

} cmplx;

float mag(cmplx x){

float y;y = sqrtf(x.real*x.real+x.imag*x.imag);

return y; }

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Functions (2)


cmplx y;

y.real = 1.0;y.imag = 1.0;

y.mag = mag(y);printf("The magnitude of %+.3f %+.3f * j is %f\n", y.real, y.imag, y.mag);

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Functions (3)

• Functions with array input variables: ex_p2_10.c

• Example: ex_p2_10.cint n, N = 4;float z[4] = {1.2, 1.1, 0.9, 0.9}, average;

printf("The mean of z is %f\n", mean(z,N));

float mean(float x[], unsigned long N){

int n;float avg = 0.0;

for (n = 0; n < N; n++)avg += x[n];

return avg / ((float)N);}

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Functions (4)

• Functions using global variables: ex_p2_11.c

// x[] and N are global variables (above the main function)float mean(){

int n;float avg = 0;

for (n = 0; n < N; n++)avg += x[n];

return avg / ((float)N);

}

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Pointers (1)

• A pointer is a variable that points to (references)a memory location where data is stored.

• Pointer declarations examples: ex_p2_12.c

float *p1, *p2;int *p3;

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0 1 2 3 4 5 6 7 8 9 10 …..

9

Computer memory

Pointers (2)

• Address operator: &

int y = 5;int *yPtr;

yPtr = &y; // yPtr gets address of y // yPtr “points to” y

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yPtr y

51000

location 800 location 1000

Pointers and Arrays


float *p1 = NULL, x[5] = {0.1, 0.2, 0.3, 0.4, 0.5}, y1, y2;p1 = &x[0]; // point p1 to the first element of x[]y1 = *(p1+3); // Equivalent to y1 = x[3]y2 = p1[3]; // Equivalent to y2 = x[3]

printf("y1 = %f\n", y1);printf("y2 = %f\n", y2);

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Bitwise Operators (1)

Type Range SymbolLogical Operators bitwise complement ~ bitwise AND & bitwise OR | bitwise XOR ^

Shift Operators left shift << right shift >>

Bitwise Operators (2)

• Example 1: ex_p2_14.c

• Example 2: ex_p2_15.cunsigned short int a = 1, b = 5;

//Bitwise operationsprintf("~a = %hu\n", ~a);printf("a & b = %u\n", a&b);printf("a | b = %u\n", a|b);printf("a ^ b = %u\n", a^b);

unsigned int a = 0, b = 3;

//Left/right shiftprintf("a=%u\n", a);a = b << 2;printf("a=%u\n", a);a >>= 1;printf("a=%u\n", a);

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Review Exercise 3

• Write a program that generates into an arraya linear frequency modulated chirp as follows:Start frequency: f0 = 1 kHzStop frequency: f1 = 2 kHzSampling frequency: fs = 48 kHzDuration: Td = 50 msThe chirp formula is given as:

• Plot the generated signal in Matlab

• Use both for, while, as well as the do approaches

y (t)=cos [2π(f 0 t+f 1−f 0

2T dt 2)]

Review Exercise 4

• Extend the structure for the complex numbers toinclude the phase argument of a complex number. Write a function, cphi, that computes phase argumentof a complex number.

• Write 4 functions that implement addition, subtraction, multiplication and division for complex numbers with names cadd, csub, cmul, and cdiv. Test the functions for z1=-1+j and z2=2j.

c tutorial - newcastle university...first example (using gcc) • example: ex_p1_1.c• read...

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