C Programming: Example C Program to Understand Functions

#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);
}