pong1.cpp

#include <iostream>
#include <SDL2/SDL.h>
#include <SDL2/SDL_mixer.h>
#include <SDL2/SDL_image.h>

using namespace std;

SDL_Texture* LoadTexture(SDL_Renderer* render, const char* name);
bool processInput(bool b[4]);

int main (int argc, char* args[]) {
    const int screen_width = 640;
    const int screen_height =480;
    bool b[4] = {0,0,0,0};
    SDL_Init(SDL_INIT_EVERYTHING);
    
    SDL_Window* window = NULL;
    window = SDL_CreateWindow("Pong", 100, 100, screen_width, screen_height, SDL_WINDOW_SHOWN | SDL_WINDOW_RESIZABLE );
    
    if (window == NULL) {
        cout << "Window load Error!" << endl;
        exit(1);
    }
    
    SDL_Renderer* render = NULL;
    render = SDL_CreateRenderer(window, -1, 0);
    
    if(render == NULL) {
        cout << "Rendering Error!" << SDL_GetError() << endl;
        exit(1);
    }
    
    SDL_Texture* stage1_image = NULL;
    stage1_image = LoadTexture(render,"stage1.png");
    
    SDL_Rect stage1_rect;
    stage1_rect.x = 10;
    stage1_rect.y = 10;
    stage1_rect.w = screen_width;
    stage1_rect.h = screen_height;
    
    SDL_Texture* red_bar_image = NULL;
    red_bar_image = LoadTexture(render, "redbar.png");
    
    SDL_Rect red_bar_rect;
    red_bar_rect.x = 10;
    red_bar_rect.y = 240;
    red_bar_rect.w = 50;
    red_bar_rect.h = 50;
    
    SDL_Texture* blue_bar_image = NULL;
    blue_bar_image = LoadTexture(render, "bluebar.png");
    
    SDL_Rect blue_bar_rect;
    blue_bar_rect.x = 580;
    blue_bar_rect.y = 240;
    blue_bar_rect.w = 50;
    blue_bar_rect.h = 50;
    
    SDL_Texture* ball_image = NULL;
    ball_image = LoadTexture(render, "ball.png");
    
    SDL_Rect ball_rect;
    ball_rect.x = 320;
    ball_rect.y = 240;
    ball_rect.w = 75;
    ball_rect.h = 50;
    
    //MainEvent is to poll event in wile loop
    while(processInput(b)) {
        
        if(b[0]) {
            red_bar_rect.y -= 3;
        }
        if (b[1]) {
            red_bar_rect.y += 3;
        }
        if(b[2]) {
            blue_bar_rect.y -= 3;
        }
        if(b[3]) {
            blue_bar_rect.y += 3;
        }

        ball_rect.x -= 5;
        
        if (ball_rect.x <= red_bar_rect.x) {
            ball_rect.x = 320;
        }

        SDL_RenderClear(render);
        SDL_RenderCopy(render, stage1_image, NULL, &stage1_rect);
        SDL_RenderCopy(render, red_bar_image, NULL, &red_bar_rect);
        SDL_RenderCopy(render, blue_bar_image, NULL, &blue_bar_rect);
        SDL_RenderCopy(render, ball_image, NULL, &ball_rect);
        SDL_RenderPresent(render);
    }
    
    SDL_DestroyWindow(window);
    SDL_DestroyRenderer(render);
    SDL_DestroyTexture(stage1_image);
    SDL_DestroyTexture(red_bar_image);
    SDL_DestroyTexture(blue_bar_image);
    SDL_DestroyTexture(ball_image);
}

SDL_Texture* LoadTexture(SDL_Renderer* render, const char* name) {
    SDL_Texture* img = IMG_LoadTexture(render, name);
    if (img == NULL) {
        cout << "Error Loading Texture: " << SDL_GetError() << endl;
        exit(1);
    }
    return img;
}

bool processInput(bool b[4]) {
    static SDL_Event* mainevent = new SDL_Event();

    while (SDL_PollEvent(mainevent)) {
        switch (mainevent->type) {
            case SDL_QUIT:
                return false;
                break;
            case SDL_KEYDOWN:
                switch(mainevent->key.keysym.sym) {
                    case SDLK_w:
                        b[0] = 1;
                        break;
                    case SDLK_s:
                        b[1] = 1;
                        break;
                    case SDLK_o:
                        b[2] = 1;
                        break;
                    case SDLK_l:
                        b[3] = 1;
                        break;
                    case SDLK_ESCAPE:
                        return false;
                        break;
                }
                break;
            case SDL_KEYUP:
                switch(mainevent->key.keysym.sym) {
                    case SDLK_w:
                        b[0] = 0;
                        break;
                    case SDLK_s:
                        b[1] = 0;
                        break;
                    case SDLK_o:
                        b[2] = 0;
                        break;
                    case SDLK_l:
                        b[3] = 0;
                }
                break;
            
        }
    }
    return true;
}

oh ok i see i had
bool b[4] = {0,0,0,0};
and you prototyped it.