C Programming: Example C Program to Understand Functions

This C program serves as a basic example for a novice C programmer to understand function usage and structure. This C source code defines a set of functions that perform various mathematical operations. These operations include calculating the square of a number, reading an integer from the user, and computing the area of a rectangle. The main function of the program calls these functions with specific values and prints the results.

We have written this code to adhere to modern C coding standards such as proper function declarations, indentation, and the inclusion of the necessary header file for input/output operations.

#include <stdio.h>

/* 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()); // Using 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
    return 0;
}

/* 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 height h */
int area(int b, int h) {
    return (b * h);
}

#include <stdio.h>

/* 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()); // Using 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

return 0;

}

/* 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 height h */

int area(int b, int h) {

return (b * h);

}

Output of the C Program:

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