Demonstrating how to use gnu make.

main.c

#include <stdio.h>
#include "ops.h"

int main(){
    
    int x = 10;
    int y = 5;

    int valA = add(x, y);
    int valS = sub(x, y);
    int valM = mul(x, y);
    int valD = div(x, y);

    printf("x = 10, y = 5 \n\n");

    printf("x + y = %i \n", valA );
    printf("x - y = %i \n", valS );
    printf("x * y = %i \n", valM );
    printf("x / y = %i \n", valD );   

    return 0;
}

Makefile

CC=gcc # compiler

all: mainapp

mainapp: main ops
     $(CC) main.o ops.o -o prog

main:
     $(CC) -c main.c

ops: 
    $(CC) -c ops.c

run:
    ./prog

clean:
    rm *.o prog

ops.c

int add(int x, int y){
    return x + y;
}

int sub(int x, int y){
    return x - y;
}

int mul(int x, int y){
    return x * y;
}

int div(int x, int y){
    return x / y;
}

ops.h

// addition 
int add(int x, int y);

// subtraction
int sub(int x, int y);

// multiplication
int mul(int x, int y);

// division
int div(int x, int y);