c - OpenGL how to set a shader texture from the program (sampler2D)

Question

I want to combine 2 textures in a GLSL shader to 1.

the problem is that I fail to set the sampler2D in the shader from my program. (the shader/program compiles correctly, the textures load correctly, the vertex shader is correct too) I tried it with the following code from a tutorial:

glUniform1i(program.getUniformLocation("Texture0"), 0);
glUniform1i(program.getUniformLocation("Texture1"), 1);

//texture 0, first texture
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, colorTexture.handle);

//texture 1, other texture
glActiveTexture(GL_TEXTURE1);
glBindTexture(GL_TEXTURE_2D, normalTexture.handle);

the fragment shader code looks like this

uniform sampler2D Texture0;
uniform sampler2D Texture1;

void main(void)
{
    vec4 color = texture2D(Texture0, vec2(gl_TexCoord[0]));
    vec4 normal = texture2D(Texture1, vec2(gl_TexCoord[0]));
    gl_FragColor = normal + color;
}

it gets drawn with

glUseProgram(program.handle);
glColor3f(1, 1, 1);
    glBegin(GL_QUADS);
    glTexCoord2f(0, 0);
    glVertex3f(0, 0, 0);
    glTexCoord2f(1, 0);
    glVertex3f(500, 0, 0);
    glTexCoord2f(1, 1);
    glVertex3f(500, 500, 0);
    glTexCoord2f(0, 1);
    glVertex3f(0, 500, 0);
    glEnd();

Answer 1

try changing the second sampler to use gl_TexCoord[1]

uniform sampler2D Texture0;
uniform sampler2D Texture1;

void main(void)
{
    vec4 color = texture2D(Texture0, vec2(gl_TexCoord[0]));
    vec4 normal = texture2D(Texture1, vec2(gl_TexCoord[1]));
    gl_FragColor = normal + color;
}