[CWC logo] C Example Programs

This document contains numerous example programs to provide a practical aid for learning C programming language.

Input and Output programs

This section contains example programs demonstrating the input and output functions.

This program uses the scanf function.

#include <stdio.h>

main()
{
    float a , b , c;
    printf("Input two numbers... \n");
    scanf("%f%f" , &a , &b);
    c  =  a * b ;
    printf("%f times %f = %f\n" , a , b , c);
}
This program combines printf and scanf whereby printf displays the input from scanf.

#include <stdio.h>

main()
{
    int i;
    printf("%c\n",scanf("%i",i));
}
This program demonstrates the use of getchar and putchar.

#include <stdio.h>

main()
{
    char ch;

    printf("Enter some text (type a period to quit)...\n");

    do {
        ch = getchar();
        putchar(ch+1);
       } while (ch != '.');

    printf("\n\n");

    printf("Enter some text (type a period to quit)...\n");

    while ( (ch = getchar()) != '.')  putchar(ch-1);

    printf("\n\n");

}

Control Loop programs

This section contains example programs demonstrating the loop construction.

Program using char data type and simple for loop:

#include <stdio.h>  /* library header */

main()
{
    char ch;

    for (ch = 'A' ; ch <= 'z' ; ch++) printf("%c\n" , ch);
}
This program demonstrates the while loop.

#include <stdio.h>

main()
{
    int lower , upper , step;
    float fahr , celsius;

    lower = 0  ;
    upper = 300;
    step  = 20 ;

    fahr  = lower;

    while ( fahr <= upper ) {
      celsius = (5.0 / 9.0) * (fahr - 32.0);
      printf("%4.0f %6.1f\n" , fahr , celsius);
      fahr = fahr + step;
    }
}
This program uses do-while and for loop constructions and standard library mathematical functions.

#include <stdio.h>
#include 

main()
{
    int i , j , k;
    double a=10.0 , b=.0;

    do {
         printf("%f\n" , pow(a,b));  /* standard function */
         b++;
       } while (b<100);

    i = 2;

    for (j=2 ; j<100 ; j=j+2) {
      i=i*j ;
      printf("%d\n" , i);
    }
}

Conditional Execution programs

This section contains example programs demonstrating if else and select statements (also break and continue statements).

This program demonstrates the if else statement.

#include <stdio.h>

main()
{
    int a , b;

        printf("Enter two numbers: ");
        scanf("%d%d" , &a , &b);

        if (b) printf("%d\n" , a/b);
        else   printf("... cannot divide by zero\n");
}
Another example of if else statement.

#include <stdio>
#include <conio>

main()

{
  int a,b;
  char ch;
  printf("Do you want to: \n");
  printf"Add, subtract, Multiply, or Divide?\n");

  /* force user to enter valid response */
  do {
       printf("Enter first letter:  ");
       ch=getchar();
       printf("\n");
     } while (ch!='A' && ch!='S' && ch!='M'         && ch!='D');
     printf("Enter first number: ");
     scanf("%d", &a);
     printf("Enter second number:  ");
     scanf("%d", &b);

  if (ch=='A') printf("%d", a+b);
  else if (ch=='S') printf("%d", a-b);
  else if (ch=='M') printf("%d", a*b);
  else if (ch=='D' && b!=0) printf("%d", a/b);
}
The switch statement is often used to process menu commands. 

#include <stdio.h>
#include <conio.h>

main()
{
  int a,b;
  char ch;

  printf("Do you want to:\n");
  printf("Add, Subtract, Multipy, or Divide\n");
  /* force user to enter valid response */
  do (
       printf("Enter first letter:  ");
       ch =getchar();
       printf("\n");
      } while (ch!='A' && ch!='S' && ch!='M'         && ch!='D');
  printf("Enter first number: ");
  scanf("%d", &a);
  printf("Enter second number:  ");
  scanf("%d", &b);

  switch (ch) {
     case 'A'  : printf("%d", a+b);
                 break;
     case 'S'  : printf("%d", a-b);
                 break;
     case 'M'  : printf("%d", a*b);
                 break;
     case 'D'  : if (b!=0) printf("%d", a/b);
                 break;
  }
}
The statement sequence associated with a case may be empty allowing two or more cases to share a common statement sequence. 

#include <stdio.h>
#include <conio.h>

main()
{
  char ch;
  printf("Enter the letter:  ");
  ch=getchar();

  switch(ch)  {
     case 'a' :
     case 'e' :
     case 'i' :
     case 'o' :
     case 'u' :
        printf(" is a vowel \n");
        break;
     default:
        printf(" is a consonant");
  }
}
A simple program to show the use of the continue statement.

#include <stdio.h>

main()
{
    int x ;

    for ( x=0 ; x<=100 ; x++) {
     if (x%2) continue;  /* using modulus operation */
        printf("%d\n" , x);
                          
}
This program jumps out of an infinite loop using the break statement.

#include <stdio.h>

main()
{
    int t ;

    for ( ; ; ) {
      scanf("%d" , &t)   ;
      if ( t==10 ) break ;
    }
    printf("End of an infinite loop...\n");

}

Structure and Nesting programs

This section contains example programs demonstrating nested block structures.

This program uses nested for loop construction.

#include <stdio.h>

main()
{
    int i , j;

    for (i=2 ; i<1000 ; i++) {
       for (j=2 ; j<= i/2 ; j++) 
         if (!(i%j)) break;
       if (j>i/2) printf("%d is a prime\n" , i);
    }
}
This example program uses a do-while and nested if else construction.

#include <stdio.h>

main()
{
    int a , b;

    do {

         printf("Enter first number: ");
         scanf("%d" , &a);
         printf("Enter second number: ");
         scanf("%d" , &b);

         if (a<b)
           printf("First number is less than second\n\n");
         if (b<a)
           printf("Second number is less than first\n\n");

        } while (a < 999);
}
This program uses nested for loop and if else construction.

#include <stdio.h>
#include <conio.h>

main()
{
  int answer, count, chances, right;
  for (count=1; count<11; count++) {
    printf("What is %d + %d?", count, count);
    scanf("%d", &answer);
    if (answer == count+count) printf("Right!\n");
    else {
           printf("Sorry, you're wrong \n");
           printf("Try again\n");
           right = 0;
           /* nested for *?
           for (chances=0; chances<3 && ! right;              chances++){
              printf("\nWhat is %d + %d?",count, count);
              scanf("%d", &answer);
              if (answer == count+count){
                printf("Right!\n");
                right=1;
              }
            }
            /* if answer still wrong, tell user */
            if (!right)
               printf("the answer is %d.\n", count+count);
         } /* end of else part */
  }   /* end of outter for loop */
}

Functions and Prototype programs

This section contains example programs to demonstrate the use of functions.

This is a program to demonstrate the use of functions

  1. with no parameters
  2. with parameters 
#include <stdio.h>

main()
{
    int number;

    prompt();  /*function call no parameters */
    scanf( "%d" , &number );

    factor(number);  /* function call with parameters */
}

prompt()   /* function */
{
    printf("Input a number... ");
}

factor(int t)   /* function */
{
    int sum = 1;
    int i ;

    for (i = 1 ; i <= t ; i++)
      sum = sum*i;
    printf("Factorial %d is %d\n" , t , sum);
}
Here is a volume computing program using a function prototype.

#include <stdio.h>

/* this is volume()'s prototype */
double volume(double s1, double s2, double s3);

void main()
{
  double vol;
  vol = volume(12.2, 5.67. 9.03);
  printf("Volume: %f", vol);
}

/* compute the volume of a cube. */
double volume(double s1, doublbe s2, double s3)
{
  return s1*s2*s3;
}
Recursion when applied to a computer language means that a function can call itself. An example follows:

#include <stdio.h>

void recurse(int i);

void main(void)
{
  recurse(0);
}

void recurse(int i)
{
  if (i<10) {
    recurse(i+1);
    printf("%d ",i);
  }
}
This program prints

9876543210

on the screen.

Array programs

This section contains example programs demonstrating the use of arrays.

A simple program to demonstrate the definition and use of an array.

#include <stdio.h>

main()
{
    int i[10],j;

    for ( j=0 ; j<10 ; j++) 
      i[j] = j ;

    for ( j=0 ; j<10 ; j++) 
      printf("%d\n" , i[j]) ;
}
A program to demonstrate the use of an array.

#include <stdio.h>
#include <stdlib.h>

main()
{
    int i , min_value , max_value ;
    int list[10] ;

    for ( i=0 ; i<10 ; i++) 
      list[i] = rand() ;

/* Find the minimum value  */

    min_value = 32767 ;

    for ( i=0 ; i<10 ; i++) 
      if (list[i]<min_value) 
        min_value=list[i] ;
    printf("Minimum value generated is %d\n" , min_value) ;

/*  Find the maximum value  */

    max_value = 0 ;

    for ( i=0 ; i<10 ; i++) 
      if (list[i]>max_value) 
        max_value=list[i];
    printf("Maximum value generated is %d\n" , max_value) ;

}
This program uses a bubble sort.

#include <stdio.h>
include <stdlib.h>

main()
{
  int item[100];
  int a,b,t;
  int count;
  /* read in numbers */
  printf("How many numbers ?");
  scanf("%d", &count);
  for (a=0;a<count;a++) scanf("%d", &item[a]);

  /* now sort using bubble sort */
  for (a=1; a<count; a++)
    for (b=count-1; b>=a; --b) {
      /* compare adjacent elements */
      if (item[b-1] > item[b]) {
        /* exchange elements */
        t= item[b-1];
        item[b-1] - item[b];
        item[b] = t;
      }
     }
     /* display sorted list */
     for (t=0; t<count; t++)  printf("%d ", item[t]);
}
An example program using a two-dimensional array now follows.

#include <stdio.h>

main()
{
  int twod[4][5];
  int i,j;

  for(i=0; i<4; i++)
    for(j=0; j<5; j++)
       twod[i][j] = i*j;

  for (i=0; i<4; i++)  {
    for (j=0; j<5; j++)
      printf("%d !, twod[i][j]);
    printf("\n");
  }
}
The program output looks like this:


00000
01234
02468
036912

Pointer programs

This section contains example programs demonstrating the use of pointers.

An example program using simple pointers.

#include <stdio.h>

main()
{
    int balance;
    int *address;
    int value;

    balance = 5000;

    address = &balance;
    value   = *address;

    printf("Balance is : %d\n" , value);
}
Another example using pointers.

#include <stdio.h>

main()
{
    int *p , num;

    p = #

    *p = 100;

    printf("%d\n" , num);
    (*p)++;
    printf("%d\n" , num);
    (*p)--;
    printf("%d\n" , num);

}
An example program demonstrating pointer Arithmetic.

#include <stdio.h>

main()
{
    char *c , ch[10];
    int  *i , j[10];
    float *f , g[10];
    int x;

    c = ch;
    i = j;
    f = g;

    for ( x=0 ; x<10 ; x++ )
      printf("%p %p %p\n" , c+x , i+x , f+x);

}
An example program using pointers and arrays.

#include <stdio.h>

main()
{
    char str[80];
    char token[10];
    char  *p , *q;

    printf("Enter a sentence: ");
    gets(str);

    p = str;

    while (*p) {
      q = token;
      while (*p != ' ' && *p) {
        *q = *p;
        q++ ; p++;
      }
      if (*p) p++;
      *q = '\0';
      printf("%s\n" , token);
    }
}

String programs

This section contains example programs to demonstrate the use of strings.

A simple string example.

#include <stdio.h>

main()
{
    char str[80] ;

    printf("Enter a string: ") ;
    gets(str) ;
    printf("%s" , str);

    printf("\n");
}
The follow program requests the input of two strings, then demonstrates the four string functions with them.

#include <string.h>
#include <stdio.h>

main()
{
  char str1[80], str2[80];
  int i;

  printf("Enter the first string:  ");
  getstr(str1);
  printf("Enter the second string:  ");
  getstr(str2);

  /* see how long the strings are */
  printf("%s is %d chars long\n", str1, strlen(str1));
  printf("%s is %d chars long\n", str2, strlen(str2));

  /* compare the strings */
  i= strcmp(str1, str2);
  if (!i) printf("The strings are equal.\n");
  else if (i<0) printf ("%s is less than %s\n", str1,str2);
  else printf("%s is greater than %s\n", str1, str2);

/* concatenate str2 to end of str1 if there is enough room*/
  if (strlen(str1)+ strlen(str2) < 80) {
    strcat(str1, str2);
    printf("%s\n", str1);
  }

  /* copy str2 to str1 */
  strcpy(str1, str1);
  printf("%s %s\n", str1, str2);
}

Structure programs

This section contains example programs to demonstrate the use of structures.

This program stores data in a structure and displays the values.

#include <stdio.h>

void main(void)
{
  struct s_type {
    int i;
    int j;
  } s;

  int i;

  i=10;
  s.i=100;
  s.j=101;

  printf("%d %d %d", i, s.i, s.j);
}
The variable i and the structure element i have no relationship to each other.

A function may return a structure to the calling procedure. 

#include <stdio.h>

struct s_type {
   int i;
   double d;
} var1;

struct s-type f(void);

void main(void)
{
  var1=f();
  printf("%d %1f", var1.i, var1.d);
}

struct s_type f(void)
{
  struct s_type temp;

  temp.i=100;
  temp.d = 123.23;

  return temp;
}
This program passes a structure to a function.

#include <stdio.h>

struct s_type {
   int i;
   double d;
} var1;

void f(struct s_type temp);

void main(void)
{
  var1.i=99;
  var1.d = 98.6;
  f(var1);
}

void f(struct s_type temp)
{
  printf("%d %1f", temp.i, temp.d);
}
The following program illustrates how to use a pointer to a structure.

#include <stdio.h>
#include <string.h>

strct s_type {
  int i;
  char str[80];
} s, *p;

void main(void)
{
  p= &s;

  s.i = 10; /* this is functionally the same */
  p ->i=10; /* as this */
  strcpy(p->str, "I like structures");

  printf("%d %d %s", s.i, p->1, p->str);
}

File Handling programs

This section contains programs demonstrating file handling and command line arguments.

The following program reads a text file and counts how many times each letter from 'A' to 'Z' occurs and displays the results.

#include <stdio.h>
#include <stdlib>
#include <ctype.h>

int count[26];

void main(int argc, char *argv[])
{
  FILE *fp;
  char ch;
  int i;
  /* see if file name is specified */
  if (argc!=2) {
    printf("File name missing");
    exit(1);
  }

  if ((fp= fopen(agv[1], "r")) == NULL) {
     printf("cannot open file");
     exit(1);
  }

  while ((ch=fgetchar(fp)) !=EOF) {
    ch = toupper(ch);
    if (ch>='A' && ch<='Z') count[ch-'A']++;
  }

  for (i=0; i<26; i++)
    printf("%c occurred %d times\n", i+'A', count[i]);

  fclose(fp);
}
This program uses command line arguments to read and display the contents of a file supplied as an argument.

#include <stdio.h>

#define CLEARS 12   /* constant */

main(int argc , char *argv[])
{
     FILE *fp , *fopen();
     int c;

     putchar(CLEARS);  

     while ( --argc > 0 )
         if ((fp=fopen(argv[1], "r"))==NULL)       
           {
             printf("I can't open %s\n", argv[1]);
             break;
           }
         else
           {
             while ((c= getc(fp)) !=EOF) 
               putc(c,stdout);  /* display to the screen */
             fclose(fp);
           }
}
This program gives a further example of the use of argc & argv

#include <stdio.h>
#include <stdlib.h>

main(int argc , char *argv[])
{
    double a , b;

    if (argc != 3) {
     printf("Usage: add number number ...\n");
     exit(1);
    }

    a = atof(argv[1]);
    b = atof(argv[2]);

    printf("%lf\n" , a + b);
}

Complex programs combining sections

This example program creates and accesses a simple database.



/**********************************************************/
/*          A simple Data Base Program                    */
/**********************************************************/

# include <stdio.h>
# include <stdlib.h>
# include <string.h>

# define MAX 100  /* constant*/

struct addr {                  /*struct called list*/
             char name[30]   ;
             char street[40] ;
             char town[20]   ;
             char county[20] ;
             char code[10]   ;
            } list[MAX];       /* 100 records*/

main()
{
    int choice;

    init_list();      /* initialze the list */

    for(;;) {
      choice = menu_select();    /* get user's selection*/        switch(choice) {
        case 1: enter();         /* enter a new entry */
                break;
        case 2: del();           /* delete an entry */
                break;
        case 3: show_list();     /* display the list */
                break;
        case 4: search();        /* find an entry */
                break;
        case 5: save();          /* save to disk */
                break;
        case 6: load();          /* read from disk */
                break;
        case 7: exit(0);
      }
    }
}

/*********************************************************/
/*         Function del                                  */
/*********************************************************/
del()
{
    int i;
    char str[255];

    inputs("enter name: " , str , 30);
    i = find(str);
    if (i>=0) *list[i].name = '\0'   ;
    else      printf("not found\n")  ;
}


/**********************************************************/
/*                   Function display                     */
/**********************************************************/
display(int i)
{
    printf("%s\n" , list[i].name);
    printf("%s\n" , list[i].street);
    printf("%s\n" , list[i].town);
    printf("%s\n" , list[i].county);
    printf("%s\n" , list[i].code);
}

/**********************************************************/
/*                     Function enter                     */
/**********************************************************/
enter()
{
    int i;

    for(;;) {
      i = find_free();        /* find a free structure */
      if(i<0) {
        printf("list full\n");
        return;
      }
      inputs("enter name: ", list[i].name,30);        if(!*list[i].name) break;      /* stop entering */
      inputs("enter street: ", list[i].street, 40);
      inputs("enter town: ", list[i].town, 20);
      inputs("enter county: ", list[i].county, 20);
      inputs("enter Postal code: ", list[i].code, 10);
    }
}

/**********************************************************/
/*                       Function find                    */
/**********************************************************/
find(char *name)
{
    int i;  
    for(i=0 ; i=count) printf("\ntoo long\n");
       } while(strlen(str)>=count);

    strcpy(s , str);
}

/**********************************************************/
/*                         Function load                  */
/**********************************************************/
load()
{
    FILE *fp;

    if ( (fp=fopen("mlist" , "rb")) == NULL) {
       printf("cannot open file\n");
       return;
    }
    printf("\nloading file\n");
    fread(list , sizeof list , 1 , fp);
    if (ferror(fp)) 
       printf("An error occurred while reading file.\n");
    fclose(fp);
}

/**********************************************************/
/*                          Function menu_select          */
/**********************************************************/

menu_select()
{
    char s[80];
    int c;
    printf("1. Enter a name\n")  ;
    printf("2. Delete a name\n") ;
    printf("3. List the File \n");
    printf("4. Search\n")        ;
    printf("5. Save the file\n") ;
    printf("6. Load the file\n") ;
    printf("7. Quit\n")          ;

    do {
        printf("\nEnter your choice: ");
        gets(s);
        c = atoi(s);
       } while(c<0 || c>7);

    return c;
}

/**********************************************************/
/*                      Function save                     */
/**********************************************************/
save()
{
    FILE *fp;

    if ( (fp=fopen("mlist" , "wb")) == NULL) {
      printf("cannot open file\n");
      return;
    }
    printf("\nsaving file\n");
    fwrite(list , sizeof list , 1 , fp);
    if (ferror(fp)) 
      printf("An error occurred while writing file.\n");
    fclose(fp);
}

/**********************************************************/
/*                        Function search                 */
/**********************************************************/
search()
{
    int i;
    char name[30];

    inputs("enter name to find: " , name , 30);
    if ((i=find(name))<0) 
      printf("not found\n");
    else display(i);
}

/**********************************************************/
/*                         Function show_list             */
/**********************************************************/
show_list()
{
    int i;

    for(i=0 ; i<MAX ; i++) {
      if(*list[i].name) {
        display(i);
        printf("\n\n");
      }
    }

    printf("\n\n");
}
[program]

The second example program uses functions to play a simple game of tic tac toe.

#include <stdio.h>
#include <stdlib.h>

char matrix[3][3];

main()
{
     char done;

     printf("This is the game of tic tac toe...\n");
     printf("You will be playing against the computer.\n") ;

     done = ' ';

     init_matrix();

     do {
         disp_matrix();
         get_player_move();
         done = check();
         if (done != ' ') break;
         get_computer_move();
         done = check();
        } while (done == ' ');

     if    (done == 'X') printf("\n\nYou won!!!\n");
     else  printf("I won!!!\n");

     disp_matrix();
}

/**********************************************************/
/*            fuction to initialise matrix                */
/**********************************************************/     
init_matrix()
{
    int i , j ;

    for (i=0 ; i<3 ; i++)
        for (j=0 ; j<3 ; j++) 
          matrix[i][j] = ' ';
}

/**********************************************************/
/*            fuction to get players move                 */
/**********************************************************/ 
get_player_move()
{
    int x , y ;

    printf("Enter coordinates of your X:  ");
    scanf("%d%d" , &x , &y);

    x--;   y--;

    if (matrix[x][y] != ' ') {
       printf("Invalid move, try again...\n");
       get_player_move();
    }
    else  matrix[x][y] = 'X';
}

/**********************************************************/
/*            fuction to get computer move                */
/**********************************************************/ 
get_computer_move()
{
    int i , j ;

    for (i=0 ; i<3 ; i++) {
       for (j=0 ; j<3 ; j++) 
          if(matrix[i][j]==' ') break;
       if (matrix[i][j] == ' ') break;
    }
    if (i*j == 9) {
       printf("draw....\n");
       exit(0);
    }
    else   matrix[i][j] = 'O';
}

/**********************************************************/
/*            fuction to display matrix                   */
/**********************************************************/ 
disp_matrix()
{
    int t ;

    printf(" 1   2   3\n");

    for (t=0 ; t<3 ; t++) {
       printf(" %c | %c | %c  %d" , matrix[t][0],
                matrix[t][1], matrix[t][2] , t+1);
       if (t!=2) printf("\n---|---|---\n");
    }
    printf("\n");
}

/**********************************************************/
/*            fuction to check matrix                     */
/**********************************************************/ 
check()
{
    int i ;

    for (i=0 ; i<3 ; i++)
       if(matrix[i][0] == matrix[i][1] && matrix[i][0] ==        matrix[i][2])
          return matrix[i][0];

    for (i=0 ; i<3 ; i++)
       if(matrix[0][i] == matrix[1][i] && matrix[0][i] ==        matrix[2][i])
          return matrix[0][i];

    if(matrix[0][0] == matrix[1][1] && matrix[1][1] ==     matrix[2][2])
          return matrix[0][0];

    if(matrix[0][2] == matrix[1][1] && matrix[1][1] ==     matrix[2][0])
          return matrix[0][2];

    return ' ';
}
[program]

[Leicester University] [] Computer Centre
Information Suppliers: Richard Mobbs, Head of Information Services, Leicester University Computer Centre and Marina Carter, Postgraduate Student, Loughborough University.
Last Updated: September 1995