Examples of function declarations, definitions, and use

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#include 
/* Examples of declarations of functions */

void square1(void);   /* Example of a function without input parameters
     and without return value */

void square2(int i);  /* Example of a function with one input parameter
                         and without return value */

int square3(void);    /* Example of a function without input parameters
                         and with integer return value */

int square4(int i);   /* Example of a function with one input parameter
    and with integer return value */

int area(int b, int h); /* Example of a function with two input parameters
      and with integer return value */

/* Main program: Using the various functions */
int main (void) {
   square1();    /* Calling the square1 function */
   square2(7);   /* Calling the square2 function using 7 as actual
      parameter corresponding to the formal parameter i */
   printf("The value of square3() is %d\n", square3()); /* Ysing the square3
          function */
   printf("The value of square4(5) is %d\n", square4(5)); /* Using the square4
   function with 5 as actual parameter corresponding to i */
   printf("The value of area(3,7) is %d\n", area(3,7)); /* Using the area
                 function with 3, 7 as actual parameters corresponding
   to b, h respectively */
}


/* Definitions of the functions */


/* Function that reads from standard input an integer and prints
   it out together with its sum */
void square1(void){
  int x;


  printf("Please enter an integer > ");
  scanf("%d", &x);
  printf("The square of %d is %d\n", x, x*x);
}


/* Function that prints i together with its sum */
void square2(int i){
  printf("The square of %d is %d\n", i, i*i);
}


/* Function that reads from standard input an integer and returns
   its square */
int square3(void){
  int x;
  printf("Please enter an integer > ");
  scanf("%d", &x);
  return (x*x);
}


/* Function that returns the square of i */
int square4(int i){
  return (i*i);
}


/* Function that returns the area of the rectangle with base b
   and hight h */
int area(int b, int h){
  return (b*h);
}


/* The output of this program is:


Please enter an integer > 3
The square of 3 is 9
The square of 7 is 49
Please enter an integer > 4
The value of square3() is 16
The value of square4(5) is 25
The value of area(3,7) is 21


*/