Considerations.c

// Your project is amazing. Thanks for it. Here goes my considerations:

/* The first thing that called my attention was that you had 4 warnings on your project.
 * I want you to understand that warnings are in fact possible future runtime errors, thus
 * we need to try to solve them before shipping a product.
 * 
 * After that, one other thing that I saw as I opened your project was that you did not quite
 * choose good names for your different files. I am saying that because they are arranged as 
 * function names, for example: Start_Game.c should call main.c, or only game.c, as the names
 * should be easy to be identified by any programmer. Other example would be the 'Print_Matrix.c',
 * I imagine that this file should call 'MatrixHelper.c' or something else, but 'Print_Matrix' is
 * a function's name rather than a class' one. Imagine that files should be treated as classes, even though
 * C does not have the abstraction of them. Also, pattern is one of our most important skills, therefore,
 * you should keep either 'CamelCase' or 'Camel_Case'. You have some files that are not compliant with the 
 * pattern of others
 */

GameLoop.c

/*
 * This file is one of your best ones. You kept it very simple and simplicity is gold.
 * One point here is that you have a 10x10 matrix and you are using the number 99 for cheating.
 * In a matrix 10x10, we have 0..9 rows and 0..9 columns, thus we can never 'hit' a ship if it ends up there.
 * It happened with me when I was testing, haha.
 * You could've used any other number greater than that, though.
 * Don't use chars for control :) use booleans(aka char) or only the values(0 and 1).
 *
 * This fseek to the end of the buffer is beautiful! Congrats!
 */

#include "GameLoop.h"

void startTheGame() {
    char shallExitGame = 'N';
    unsigned int userI, userJ, oneNumber;
    unsigned int n;

    printf("\n");
    printf("====== LET'S START SHOOTING! ======\n");
    printf("= (111 - Exit, 99 - See the ships) =\n");
    printf("===================================\n\n");

    while (shallExitGame == 'N') {
        do {
        printf("Line and Column as one number: ");
        n = scanf("%d",&oneNumber);
            if (n !=1) {
                fseek(stdin,0,SEEK_END);
                printf("Sorry! Did not capture your enter! Please trye again!\n");
            }
        } while (n != 1);

        if (oneNumber == 111) {
            shallExitGame = 'Y';
            continue;
        }
        else if (oneNumber == 99) {
            printf("\n");
            printMatrix(0);
            printf("\n\n");
            continue;
        }

        userI = (oneNumber - oneNumber % 10)/10;
        userJ = oneNumber % 10;

        hitCheck(userI,userJ);
    }
}

GameLoop.h

/*
 * I don't know how this program is working, haha
 * Your file calls "HitCheck.h", but you are calling "hitCheck.h".
 * This must be one of XCode's tricks.
 * Remembering that Unix based systems have case sensitive paths ;)
 * Wasn't this file supposed to call "Game_Loop.h"? Stick to one pattern.
 */

#ifndef GameLoop_h

#define GameLoop_h
#include <stdio.h>
#include "Global_Data.h"
#include "Print_Matrix.h"
#include "hitCheck.h"

void startTheGame();

#endif /* GameLoop_h */

Global_Data.c

// Please see Global_Data.h

#include "Global_Data.h"

unsigned int battelFieldMatrixXY = 10;
unsigned int battleFieldMatrix[10][10] = {};
unsigned int allShipsMatrix[20] = {11,
                                   12,
                                   13,
                                   14,
                                   21,21,
                                   22,22,
                                   23,23,
                                   31,31,31,
                                   32,32,32,
                                   41,41,41,41};

Global_Data.h

/*
 * Try to not include libraries that you don't need.
 * As well as avoid as much as you can to create global variables.
 * Global variables should be used for readonly purposes.
 * http://c2.com/cgi/wiki?GlobalVariablesAreBad
 */

#ifndef Global_Data_Defined

#define Global_Data_Defined
#include <stdio.h>

extern unsigned int battelFieldMatrixXY;
extern unsigned int battleFieldMatrix[10][10];
extern unsigned int allShipsMatrix[20];

#endif

HitCheck.c

/*
 * You should have included "HitCheck.h" oO
 * If you have smaller statements, you won't need things like:
 * //end (battleFieldMatrix[i][j] != 0)
 * 
 * Use enums in your switches and returns :) They are very nice.
 */
 
#include "hitCheck.h"

void hitCheck(unsigned int i, unsigned int j) {
    unsigned int shipHit;

    if (battleFieldMatrix[i][j] != 0 && battleFieldMatrix[i][j] != 77) {
        shipHit = battleFieldMatrix[i][j];

        battleFieldMatrix[i][j] = 77;

        switch (findShip(shipHit)) {
        case 0:
                printf("\n");
                printf("======== TOTAL ANNIHILATION! ======\n");
                printf("===== DESTROYED SHIP'S SIZE: %d ====\n\n", (shipHit-shipHit%10)/10);
                break;
        case 1:
                printf("\n");
                printf("======== YOU GOT A PIECE! =========\n\n");
                break;

        case 2:
                printf("\n");
                printf("======== ABSOLUTE VICTORY! ========\n\n");
                printMatrix(1);
                exit(0);
                break;
        }
    }
    else {
        printf("\n");
        printf("============= MISSS! ==============\n\n");
    }

    printMatrix(1);

}

int findShip(unsigned int shipNumber) {
    static unsigned int controlSum = 77*20;

    for (unsigned int i=0;i<20;i++) {

        if (allShipsMatrix[i] == shipNumber) {

            allShipsMatrix[i] = 77;

            controlSum-=77;
            if (controlSum == 0) return 2;

            switch (i) {
                case 19:
                    return 0;
                default:
                    if (allShipsMatrix[i+1] == shipNumber ) {
                        return 1;
                    }
                    else {
                        return 0;
                    }
            }
        }
    }
    return 5;
}

HitCheck.h

/*
 * Wasn't this file supposed to call "Hit_Check.h"?
 */

#ifndef hitCheck_h
#define hitCheck_h

#include <stdio.h>
#include <stdlib.h>
#include "Global_Data.h"
#include "Print_Matrix.h"

void hitCheck(unsigned int i, unsigned int j);

#endif /* hitCheck_h */

Place_Ships.c

/*
 * Try to use spaces after assignments and operations in order of better legibility, like:
 * checkSumForSurraundings += battleFieldMatrix[i][leftJ];
 * instead of
 * checkSumForSurraundings+=battleFieldMatrix[i][leftJ];
 *
 * The software designers/architects also say that each function/method should be at maximum your screen's height,
 * so you should probably break the function 'placeShips' down in smaller ones.
 * I invite you to take a look to this code here: https://github.com/luizperes/artoo-editor/tree/master/src
 *
 * Instead of 'f' or 't' you should have included the stdbool.h, although they are both 1 byte long.
 * 
 * Nested switches are not as good as breaking it down in functions. They are very hard to understand.
 * Try to include blocks { } as well, you can put them anywhere in order to ease readability.
 * 
 * It is not a good practice to leave 'ifs' as: 
 * if(something) break;
 *
 * Apple itself had a very bad security whole because of one if like that:
 * if (something)
 *    DoIt;
 *    DoAnotherThing;
 *
 * DoAnotherThing does not belong to the if, so many programmers have the curly braces as a programming
 * standard. Swift itself does not allow us to not use braces. Perhaps because of that previous failure?
 *
 * Always keep your statements like the one on the line below.
 *  if (something) {
 *     DoIt;
 *     DoAnotherThing;
 *  }
 *
 * For Switches, try to only use integers and enums instead of chars :)
 * 
 * I like your recursivity, but perhaps a for-loop wouldn't be better?
 * Remember that recursivity takes more space in memory as it forces new Stack frames 
 * (if the language does not have Tail Call Optimization, as Javascript, for example).
 * We should use recursivity carefully. In this case is fine! :)
 * 
 * I like that you used checksum! Not everyone knows that way of programming resolution.
 */

#include "Place_Ships.h"

// this function prototype must exist, because C reads and compile inline.
// You did not get an error because XCode solved this problem for you. If should do that for
// all other warnings.
int randomCell();

void placeShips(int size, int shipNumber) {
    
    /*
     * You got a warning here, because you did not define the prototype of the function
     * 'randomCell' at the top of the file
     */
    unsigned int rndCell = randomCell();
    
    int i = (rndCell - rndCell % 10)/10;
    int j = rndCell % 10;
    
    char leftOrRight;
    char upOrDown;
    
    unsigned int checkSumForShip;
    unsigned int checkSumForSurraundings;
    char endSuccessfully = 'f';
    
    int upperI, lowerI, leftJ, rightJ;
   
    switch (rand() % 3) {
        //0 - horizontal
        case 0:
            
            leftOrRight = (battelFieldMatrixXY-1)-j >= size-1 ? 'r' : 'l';
            switch (leftOrRight) {
                case 'r':
                    checkSumForShip = 0;
                    for (int r = j+1; r<=j+size-1;r++) {
                        if (battleFieldMatrix[i][r] == 0) checkSumForShip++;
                    }
                    
                    if (checkSumForShip == size-1) {
                        checkSumForSurraundings = 0;
                        upperI = i == 0 ? 0 : i-1;
                        lowerI = i == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : i+1;
                        rightJ = (j+size) > battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : j+size;
                        
                        for (int tempJ = j+2; tempJ<=rightJ;tempJ++) {
                            checkSumForSurraundings +=battleFieldMatrix[upperI][tempJ] + battleFieldMatrix[lowerI][tempJ];
                        }
                        checkSumForSurraundings+=battleFieldMatrix[i][rightJ];
                        
                        
                        if (checkSumForSurraundings == 0) {
                            for (int tempJ = j;tempJ<j+size;tempJ++) {
                                battleFieldMatrix[i][tempJ] = size*10+shipNumber;
                            }
                            endSuccessfully = 't';
                            break;
                        }
                        
                    }
                case 'l':
                    checkSumForShip = 0;
                    for (int r = j-1; (r>=j-(size-1)) && (r >0) ;r--) {
                        if (battleFieldMatrix[i][r] == 0) checkSumForShip++;
                    }
                    if (checkSumForShip == size-1) {
                        checkSumForSurraundings = 0;
                        upperI = i == 0 ? 0 : i-1;
                        lowerI = i == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : i+1;
                        leftJ = (j-size) < 0 ? 0 : j-size;
                        
                        for (int tempJ = j-2; tempJ>=leftJ;tempJ--) {
                            checkSumForSurraundings +=battleFieldMatrix[upperI][tempJ] + battleFieldMatrix[lowerI][tempJ];
                        }
                        checkSumForSurraundings+=battleFieldMatrix[i][leftJ];
                        
                        if (checkSumForSurraundings == 0) {
                            
                            for (int tempJ = j;tempJ>j-size;tempJ--) {
                                battleFieldMatrix[i][tempJ] = size*10+shipNumber;
                            }
                            
                            endSuccessfully = 't';
                            
                            break;
                        }
                    }
            }
            
            if (endSuccessfully == 't') {
                break;
            }
            
            //1 - vertical
        case 1:
            upOrDown = (battelFieldMatrixXY-1)-i >= size-1 ? 'd' : 'u';
            switch (upOrDown) {
                case 'd':
                    checkSumForShip = 0;
                    for (int r = i+1; r<=i+size-1;r++) {
                        if (battleFieldMatrix[r][i] == 0) checkSumForShip++;
                    }
                    
                    if (checkSumForShip == size-1) {
                        checkSumForSurraundings = 0;
                        lowerI = (i+size) > battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : i+size;
                        leftJ = j == 0 ? 0: j-1;
                        rightJ = j == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1: j+1;
                        
                        for (int tempI = i+2; tempI<=lowerI;tempI++) {
                            checkSumForSurraundings +=battleFieldMatrix[tempI][leftJ] + battleFieldMatrix[tempI][rightJ];
                        }
                        
                        checkSumForSurraundings+=battleFieldMatrix[lowerI][j];
                        if (checkSumForSurraundings == 0) {
                            
                            for (int tempI = i;tempI<i+size;tempI++) {
                                battleFieldMatrix[tempI][j] = size*10+shipNumber;
                            }
                        
                            endSuccessfully = 't';
                            break;
                        }
                    }
                case 'u':
                    checkSumForShip = 0;
                    for (int r = i-1; (r>=i-(size-1)) && (r >0) ;r--) {
                        if (battleFieldMatrix[i][r] == 0) checkSumForShip++;
                    }
                    if (checkSumForShip == size-1) {
                        checkSumForSurraundings = 0;
                        upperI = (i-size) < 0 ? 0 : i-size;
                        leftJ = j == 0 ? 0: j-1;
                        rightJ = j == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1: j+1;
                        
                        
                        for (int tempI = i-2; tempI>=upperI;tempI--) {
                            checkSumForSurraundings +=battleFieldMatrix[tempI][leftJ] + battleFieldMatrix[tempI][rightJ];
                        }
                        checkSumForSurraundings+=battleFieldMatrix[upperI][j];
                        
                        if (checkSumForSurraundings == 0) {
                            
                            for (int tempI = i;tempI>i-size;tempI--) {
                                battleFieldMatrix[tempI][j] = size*10+shipNumber;
                            }
                            endSuccessfully = 't';
                            
                            break;
                        }
                        
                    }
            }
            if (endSuccessfully == 't') break;
            
        default:
            placeShips(size, shipNumber);
            
    }
}

int randomCell() {
    unsigned int i;
    unsigned int j;
    int upperI, lowerI, leftJ, rightJ;
    unsigned int random;
    unsigned int checkAroundSum;
    
    while (1) {
        random = rand() % (battelFieldMatrixXY*battelFieldMatrixXY);
        i = (random - random % 10)/10;
        j = random % 10;
        checkAroundSum = 0;
        
        if (battleFieldMatrix[i][j] == 0) {
            
            upperI = i == 0 ? 0 : i-1;
            lowerI = i == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : i+1;
            leftJ = j == 0 ? 0 : j-1;
            rightJ = j == battelFieldMatrixXY-1 ? battelFieldMatrixXY-1 : j+1;
            
            checkAroundSum = battleFieldMatrix[upperI][j] +
            battleFieldMatrix[lowerI][j] +
            battleFieldMatrix[i][leftJ] +
            battleFieldMatrix[i][rightJ] +
            battleFieldMatrix[upperI][leftJ] +
            battleFieldMatrix[upperI][rightJ] +
            battleFieldMatrix[lowerI][leftJ] +
            battleFieldMatrix[lowerI][rightJ];
            
            if (checkAroundSum == 0) break;
        }
    }
    
    return i*10+j;
}

Place_Ships.h

// ========================== Place_Ships.c

#ifndef Place_Ships_h

#define Place_Ships_h

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include "Global_Data.h"

void placeShips(int size, int shipNumber);

#endif /* Place_Ships_h */

Print_Matrix.c

/*
 * Try to not use global variables, it is better to pass them around inside functions.
 * You may have trouble with them later on if another file(s) "change" their value by accident.
 * Other than that, everything here looks cool.
 */

#include "Print_Matrix.h"

void printMatrix(int mode) {
    printf("     0  1  2  3  4  5  6  7  8  9 \n");
    printf("   -------------------------------\n");

    for (int i = 0; i<battelFieldMatrixXY;i++) {
        //the start of each line with art and number
        printf("%d | ",i);
        for (int j = 0; j<battelFieldMatrixXY;j++) {
            switch (battleFieldMatrix[i][j]) {
                case 0:
                    printf(" . ");
                    break;
                case 77:
                    printf(" × ");
                    break;
                default:
                    if (mode == 0)  printf(" © ");
                    else printf(" . ");
                    break;
            }

        }
        
        printf("|\n");
    }

     printf("   -------------------------------\n");
}

Print_Matrix.h

#ifndef Print_Matrix_h
#define Print_Matrix_h

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

// try to use enums next time :)
void printMatrix(int mode);

#endif /* Print_Matrix_h */

Start_Game.c

// ========================== Start_Game.c
 
#include <stdio.h>
#include "Print_Matrix.h"
#include "Place_Ships.h"

int main(void)
{
    /* You have a warning there, saying:
     * Implicit conversion loses integer precision: 'time_t' (aka 'long') to 'unsigned int'
     * That happens because 'time_t' is not a 'unsigned int', so it is up to the programmer to do that.
     * To fix that, we would write something like srand((unsigned int) time(NULL));
     * Have in mind that 'time_t' (aka 'long') is 8 bytes long while 'unsigned int' is still 4 bytes long,
     * in this way, when you cast it to (unsigned int), the value is truncated
     */
    srand(time(NULL));
    
    placeShips(4,1);
    
    placeShips(3,1);
    placeShips(3,2);
    
    placeShips(2,1);
    placeShips(2,2);
    placeShips(2,3);
    
    placeShips(1,1);
    placeShips(1,2);
    placeShips(1,3);
    placeShips(1,4);
    
    printMatrix(1);
    
    startTheGame();
}

// You don't need to write comments like "Print the Matrix" in a function called 'printMatrix'