functions in c

nard

can somebody help me on writting a program that displays y_o
to y_n+1 when n=100 and store them in a file.
y"=cos(t)*y+y
y(0)=1
y'(0)=0
h=0.1
y'=z
z'=z'*cos(t)+y
y_n+1=z_n+h*z_n*(cos(t_n))+y_n)
t_n=t+nh

nard

i have the above using for loop without declaring any fuction,
if someone knows how to solve it including user defined function then he might be able to help me.
thank you!
the one i wrote is showed below

#include<stdio.h>
#include<math.h>
#include<stdlib.h>
main()
{
FILE *fp;
fp=fopen("D:\\cop.txt","w");
float y[100],dy[100],z[100],h,t[100];
int i;
y[0]=1;
z[0]=0;
h=0.1;
t[0]=0;
for(i=0;i<100;i++)
{
t[i]=t[0]*i*h;
y[i+1]=y[i]+h*z[i];
z[i+1]=z[i]+h*((z[i]*cos (t[i]))+y[i]);
}
fprintf(fp,"i\tz(n+1)\t\ty(n+1)\n\n");
printf("i\tz(n+1)\t\ty(n+1)\n\n");
for(i=0;i<100;i++)
{

fprintf(fp,"%d\t%f\t%f\n",i,z[i+1],y[i+1]);
printf("%d\t%f\t%f\n",i,z[i+1],y[i+1]);
}
fclose(fp);
system("PAUSE");

}