how to write function in c

1#include <stdio.h>
2
3void function(){
4  printf("I am a function!");
5}
6
7int main(void) {
8  
9  function();
10}

1#include <stdio.h>
2int addition(int num1, int num2)
3{
4     int sum;
5     /* Arguments are used here*/
6     sum = num1+num2;
7
8     /* Function return type is integer so we are returning
9      * an integer value, the sum of the passed numbers.
10      */
11     return sum;
12}
13
14int main()
15{
16     int var1, var2;
17     printf("Enter number 1: ");
18     scanf("%d",&var1);
19     printf("Enter number 2: ");
20     scanf("%d",&var2);
21
22     /* Calling the function here, the function return type
23      * is integer so we need an integer variable to hold the
24      * returned value of this function.
25      */
26     int res = addition(var1, var2);
27     printf ("Output: %d", res);
28
29     return 0;
30}
31

1#include <stdio.h>
2
3// Here is a function declaraction
4// It is declared as "int", meaning it returns an integer
5/*
6	Here are the return types you can use:
7    	char,
8        double,
9        float,
10        int,
11        void(meaning there is no return type)
12*/
13int MyAge() {
14	return 25;
15}
16
17// MAIN FUNCTION
18int main(void) {
19	// CALLING THE FUNCTION WE MADE
20    MyAge();
21}

1#include <stdio.h>
2/* function return type is void and it doesn't have parameters*/
3void introduction()
4{
5    printf("Hi\n");
6    printf("My name is Chaitanya\n");
7    printf("How are you?");
8    /* There is no return statement inside this function, since its
9     * return type is void
10     */
11}
12
13int main()
14{
15     /*calling function*/
16     introduction();
17     return 0;
18}
19