Having Trouble w/ simple graphing program; need some help

Hey guys, I started on this simple plotting program, and everything seems to be fine with the program, no errors came up, but its not plotting the graph. Here's the code, and any suggestions would be more than appreciated.

Code:

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#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#define X_SEMIRANGE 3
#define Y_SEMIRANGE 2

int rtoi(double);
double f(double);
char graph[Y_SEMIRANGE*20+1][X_SEMIRANGE*20+1];/*store x and y points in a
character array*/
int creategraph();
int plot();
int dispplot();

int main()
{
        creategraph();
        plot();
        dispplot();
        getchar();       
        return 0;
}

int rtoi(double x) /*rounds the double values of f() to ints before storing
points in the array*/
{
        int i;
        if(x >= 0)
                i = (int)(x + 0.5);
        else /* x < 0 */
                i = (int)(x - 0.5);
        return i;
} 

double f(double x) /*holds the function to be graphed. Can be easily
overwritten*/
{     
        return cos(x*x);
}
               
int creategraph()
{
        int i,j;
        for (i=0; i<=X_SEMIRANGE*20+1; i++)/*for loop defines where axes should be
    placed*/
        {
                for (j=0; j<=Y_SEMIRANGE*20; j++)
                {
                        if(i==(X_SEMIRANGE*20/2))
                                graph[j][i] = '|';
                        else if(j==(Y_SEMIRANGE*20/2))
                                graph[j][i]='-';
                        else
                                graph[j][i]=' ';/*inserts empty spaces in the array, this will
                be replaced in the the graph*/
                }
        }
}

int plot()
{
        int x_coor,y_coor;
        double range;
        double func;
        for(range=-1*((X_SEMIRANGE*20)/2); range <=((X_SEMIRANGE*20)/2); range++)
    /*for loop will plot the points onto graph, it starts from negative
    X_SEMIRANGE and goes to the end of X_SEMIRANGE*/
        {
                func = (f(range));/*units in x direction will increment by 1/10*/
                y_coor=(Y_SEMIRANGE)*20/2-rtoi(func);/*values are rounded and
        plotted where the graph is*/
                x_coor=(X_SEMIRANGE)*20+range;
                if(y_coor >= 0 && y_coor <=20*Y_SEMIRANGE)
                        graph[y_coor][x_coor]='o'; /*inserts 'o' where I previousle had
            empty spaces in the previous for loop*/
        }
}

int dispplot()
{
        int i,j;
        for(j=0; j <= Y_SEMIRANGE*20; j++)/*checks if any graph gets cut off
    by semirange*/
        {
                for(i=0; i <= (X_SEMIRANGE*20); i++)
                {
                        printf("%c",graph[j][i]);
                }
                printf("\n");
        }
}

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When a function has a data type listed on the left side of it's first line of the function, then it needs to return a data item of that type.

In this case, three functions aren't returning int values. Your compiler should be warning you about that. Just add the line:

Code:

---

return 0;

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just before the closing brace for these functions, and the program works.

With the values it displays now, the x axis is correct. The y axis center, I didn't measure, but it appears right.