I am trying to use some local variables in the glsl shade. However, everytime I simply declare or declare and assign the variable to an initial value , it seems my shader stops working properly. Before doing this , I used to get a pretty picture on my screen, now I get a blank white screen.

Code :
static const char render_fs[] =
        "#version 430 core\n"
        "layout (location = 0) out vec4 color;\n"
        "uniform sampler2D output_image;\n"
        "void main(void)\n"
	"vec4 sample=vec4(1.0,1.0,1.0,1.0};\n"
        "    color = texture(output_image, vec2(gl_FragCoord.xy) / vec2(textureSize(output_image, 0)));\n"

See the sample variable. Just adding this whites out what i see on the screen.